The handset boasts a fast processor, AMOLED screen and a camera with a Carl Zeiss lens. But is it good enough to revive Nokia as a serious player in a world of smart phones dominated by Apple, Samsung and HTC? Available now, it's around £470 SIM-free, £400 on pay as you go or free on contracts from around £25 per month.

The Lumia 800 is a stylish looking handset and its build quality is also first-rate. It's a fun phone to use, thanks to Microsoft's slick Windows Phone 7.5 software, which has excellent integration for social networking sites, such as Facebook and Twitter.

The Nokia Mix Radio streaming service may not be revolutionary, but the fact it's free and has a good selection of tunes and playlists makes it a welcome addition. We also like Nokia's Drive navigation software, especially as you can download maps to avoid incurring roaming charges when using it abroad.

The range of apps available for Windows Phone is growing steadily. Even so, you stilll won't find anywhere near as many in the Windows Phone Marketplace as you will in Apple's App Store or Android Market.

The phone's battery life is on a par with most other smart phones so you can expect to have to charge it at the end of each day. Call quality is excellent and it's good at maintaining a connection in weaker signal areas.

If you're not overly concerned with having a particularly high-resolution screen, and are willing to put up with a camera that's not quite as good as other similarly-priced smart phones, then the Lumia is a good option. This is especially true if you're looking for an alternative to the iPhone that still offers a very polished user experience.

The big difference between the Lumia 800 and previous Nokia smart phones is that this handset runs on Microsoft Windows Phone software. Naturally, it uses the latest Mango version of the operating system, which includes a number of new features, not least of which is support for multi-tasking.

Microsoft's previous mobile OS, Windows Mobile, was a mess. Thankfully the company went back to the drawing board and came up with a brand new interface. The results are very impressive. Once you've used it, it's not difficult to see why Nokia's head honcho decided to dump Symbian in favour of it.

Windows Phone looks absolutely gorgeous. Thanks to some slick 3D effects and its dynamic design, it feels more modern than even Android or iOS.

The main homescreen displays a column of live tiles that dynamically update to shows you various information. For example, the People Hub flicks through photos drawn from your social networking contacts, while the messaging and mail titles show you any unread messages you might have.

You can also pin applications, pictures, contacts and other bits and bobs to this homescreen to use as shortcuts. Swiping right reveals your full list of apps as a single scrollable list.

You can tap the search button to quickly find a particular app, or if you've got more than 44 entries in the list, Windows Phone automatically divides up your apps alphabetically so you can quickly jump to groups of apps.

 When you open an application, the titles tear away from the screen with a cool 3D flip-effect and the same happens when you leave an app to return to the home screen.

If you've got multiple apps running you can switch between them by holding down the back button. This calls up a deck of cards showing a thumbnail of all the apps currently loaded. You can then scroll over to quickly select the one you want to jump.

One of the best things about the OS is that social networking is built into the operating system. The People Hub pulls together not just all your contacts, but also feeds from Facebook, Twitter and Linked-in. What's more, conversations in the messaging app can jump between text messaging and social media messaging and Windows Phone will keep them all threaded in the same conversation.

However, the OS does have drawbacks. The Bing Maps that are integrated into the OS are pretty poor, not because they're inaccurate -- they're not -- but simply because they don't show as many street names on the standard zoom level as you get with Google Maps on Android or the iPhone.

When you can't see the name of the street where you need to turn off, it's a huge annoyance. Unfortunately it happens all the time with Bing Maps. Also the cut and paste system can be fiddly to use as the tabs for selecting text are on the small side. Another issue is that the OS doesn't yet support Adobe Flash, so you can't view videos on websites like BBC iPlayer.

The Lumia's design will bring on a sense of déjà vu for anyone who has previously seen Nokia's N9 handset. The body is hewn almost entirely from polycarbonate and is available in three colours: black, cyan and magenta. The two long edges are curved like the old iPod Nano and the back is gently sloped at the top and bottom.

The result is that the phone looks slightly oblong when viewed side-on. Despite the use of plastic for the body, it has a very premium and sturdy feel. Besides, Nokia says that the plastic casing helps the handset's phone reception.

The front is almost completely taken up with the gorilla glass that covers the screen and three Windows Phone touch buttons at the bottom. This helps to give the face a smooth, seamless look. The only physical buttons are mounted on the right-hand edge.

Here you'll find a volume rocker switch, the lock button and a dedicated camera button. One thing we love about Windows Phone handsets is that they all have dedicated camera buttons; you jump directly to the camera app, even when the phone is in standby, just by pressing and holding it down.

Nokia has placed the standard 3.5mm headphone jack at the top corner; hidden behind a flap next to it is a micro USB port that's used for both charging and syncing. Further along the top edge there's a sliding cover that -- when released -- gives you access to the SIM card slot. Like the iPhone, the Lumia uses a micro SIM, so if you have a full-sized SIM that you want to use with the phone you'll have to get it cut down to size.

The phone fits nicely in the hand and the curved edges arguably make it more comfortable to hold than the more angular iPhone 4S. Its smaller display also means that it's narrower and shorter than Samsung's S2. As a result, it feels more pocketable.

On the downside, like the iPhone 4S, the Lumia 800 is a completely closed device. You can't remove the battery and you can't add any more memory to it, as there's no microSD card slot.

Nokia has built the phone around a 1.4GHz Qualcomm MSM8255 Snapdragon processor, which includes an Adreno 205 GPU. The OS has 512MB of RAM and 512MB of ROM to play with. There's 16GB of memory for storing music, videos, photos and apps.

Those specs may seem tame next to the dual-core processors used in the iPhone 4S and Samsung Galaxy S2, but the Lumia still feels like a very quick handset. This may in some part be due to the lower demands that Microsoft's OS seems to place on a phone's hardware. Windows Phone uses hardware acceleration for its 3D menu effects, scrolling and zooming, which seems to help keep everything rollicking along at a very sprightly pace. Apps open quickly and it's speedy when jumping between them. Pages are also quickly rendered in the browser.

The Lumia also easily outdid HTC' s Radar in the Benchmark Free application. It scored 6.3 in the CPU integrate test versus the Radar's 4.7 (a higher number is better). This is perhaps not surprising given that the Radar uses a slower 1GHz chip. However, in the Javascript SunSpider Test it scored a disappointing 6,915.7ms, compared to the iPhone 4S's score of just 2,181.6ms and the Samsung Galaxy S2's 3,445.3ms (lower is better).

Call quality was, on the whole, very good. The ear piece delivers clean and crisp audio and is also loud enough to let you hear callers above the din of noisy bars or busy streets. The mic delivers impressive quality speech. The phone's reception is excellent -- it does a good job of holding on to a connection even in weaker signal areas.

In the past, Nokia phones have enjoyed a strong reputation for providing long battery life. Unfortunately that hasn't transferred across to the Lumia 800. You'll get around a day out of it before it needs a recharge, which is really no better or worse than the majority of smart phones.

The Lumia has a 3.7-inch screen which, like all of the current Windows Phone handsets on the market, has a resolution of 480x800 pixels. That's some way off the resolution of the iPhone's 4S screen. The display uses AMOLED technology similar to that used on the Galaxy S2.

There are a few benefits to AMOLED displays: they're self-illuminating so darker colours draw less power than LCD screens; they're also capable of producing very, very dark black levels. In fact, the screen produces such dark blacks that it can be difficult to see where the display ends and the bezel begins when you're on the WP7 homescreen.

The Lumia's screen's brightness levels are very high, which gives colours a really vibrant look. However, the display isn't without its problems. Like a lot of OLED screens, whites have a slightly blue-ish tinge; this is often noticeable on webpages with white backgrounds such as Google's homepage. The Lumia wasn't as blue-ish as the display on our Galaxy S2, but next to the iPhone 4S, or even just a white sheet of paper, it was still noticeably off.

Colours can appear overly peaky or a tad too vivid, but again this is an issue that also affects the Galaxy S2's AMOLED display. Some people might like the effect even though it's not as colour-accurate as other displays.

This model suffers a little from the same type of PenTile matrix problem that affected the original Samsung Galaxy S. Due to the way the screen creates coloured pixels by grouping red, blue and green subpixels together, text that is rendered very small can look speckled or blurry. It's not a massive issue but it is noticeable at certain times such as when you're looking at grey text against a white background in the browser.

When it announced its tie-up with Microsoft, Nokia made a big deal of the fact that it would be the only manufacturer that would be truly allowed to customise the OS. As such, we were interested to see what was different about the Lumia 800 compared to other Windows Phone handsets.

The answer is not all that much, at least at present. Nokia representatives were keen to point out that there's more to come in the future. Unfortunately, the Nokia Maps software was not available on our handset, although Nokia promises that it will be there once the phone is officially released in the UK.

What you do get is Nokia Drive, which offers turn-by-turn navigation, complete with voice prompts. Maps are actually downloaded to the phone and stored locally; you won't rack up roaming charges if you use it abroad as long as you've downloaded the maps beforehand. You can also download voice packs and languages if you need, and the view can be switched between 2D and 3D modes, complete with landmarks.

The other big addition is the Nokia music app. This duplicates some of the functionality of the standard Zune music app built-in to Windows Phone, in that you can use it to playback tracks that you've transfer from a PC using the Zune desktop software. It also has an on-phone music store where you can purchase and download tracks (at a cost of 99p each).

It does add a couple of extra features: the Gigs option shows you what gigs are on near you and lists the time at which they start and the venue address. Of more interest is the Mix Radio option. This lets you stream hours of music for free -- there's no subscription required and you don't even have to sign up or provide any log-in details.

You simply select a genre and you're then presented with playlists that you can listen to. For example, if you pick Rock, you'll find playlists for new rock releases, bestsellers, punk rock and 1990s alternative, among a whole load of others.

Once you select one, music will start streaming to your phone within seconds. It acts a lot like the radio features in Napster, except that you can only skip forward a track and you can only skip seven tracks within a 24-hour period. If you like a track there's a link to buy it from the music store.

The service works over 3G as well as Wi-Fi. Our test phone only supported live streaming, but Nokia says it will soon update the app to add a feature to let you cache tracks for listening offline and let you pin a playlist to your start screen. Even without these features, we really liked using Mix Radio; its selection of tracks seemed pretty comprehensive and the range of genres covered is broad.

The only other app that Nokia has added is App Highlights, which simply offers some recommendations on apps you might want to download from the Marketplace. It also alerts you when updates are available for Nokia's own apps.

When it comes to other apps, Windows Phone is found lacking compared to the competition. Whereas Apple's App Store and Android Market offer tens, if not hundreds, of apps for every conceivable task, the Windows Phone Marketplace is a relatively barren place.

For some people this may not be an issue. The OS does, after all, have built-in support for Facebook, Twitter and LinkedIn. It also comes with the excellent mobile version of Microsoft Office for creating and editing office documents.

On the plus side, since the launch of Mango, there's been a notable increase in app releases. Newsreaders like Pulse and Weave have made their way onto the platform, as well as the likes of Tesco Groceries, Groupon, Amazon Kindle, Kayak and Tripit. Nevertheless, there's a long, long way to go before we see the sheer range of apps available from Apple and Google's platforms.

Sadly Nokia hasn't added a front-facing camera to this phone. This is a shame as both of HTC's latest Windows Phone handsets, the Radar and Titan, have them. It means you can't use it to make video calls and won't be able to use the video conferencing features of Skype when Microsoft finally gets around to launching the app on Windows Phone.

We had high hopes for the main camera on the Lumia. After all, it uses Carl Zeiss Tessar optics and has an 8-megapxiel sensor. However, the camera is disappointing. It is capable of taking very good shots, but it's much fussier about having the right conditions than the snappers in the Galaxy S2 and especially the iPhone 4S.

In day-to-day use the camera is slower to focus and less reliable at getting accurate focus -- especially on close-ups -- than the iPhone 4S. It also tends to blow out highlights, indicating that its dynamic range is a little limited -- something that can be seen on both still shots and videos.

Working indoors in darker conditions without the flash, there's a tad more noise in its images than either the Galaxy S2 or the iPhone 4S. However, its flash helps out enormously and isn't as aggressive as the one on the iPhone 4S; as such, colours tend to look less washed out when you're using flash.

We benchmarked the Lumia's shots against the iPhone 4S and Galaxy S2. Click the following links to view the results:

When it comes to video recording, the Lumia 800 can record at up to 720p resolution, whereas both the iPhone 4S and Galaxy S2 have 1,080p recording modes. Nevertheless, the quality of the 720p video isn't bad and offers a good level of sharpness. However, like most of the video recording modes on today's smart phones, the more movement in the frame, the more the detail levels drop off.

The camera software is quite good. It offers a number of scene modes and supports touch-to-focus. However, we did notice a bug in the video recording mode. Often when you switch to video mode the camera will simply refuse to refocus, leaving you locked at a blurry focus setting.

You have to switch to stills mode and then back to video mode to get it to start refocusing. Another annoyance is that the camera app doesn't remember the resolution you last selected. Instead, it always defaults to 640x480 pixels. To be fair, this issue is a Windows Phone problem rather than a Nokia issue; it also happens on HTC's WP7 handsets.

Overall, the Lumia 800 is a very good handset. The Windows Phone software is slick and fun to use, especially if you like to keep up-to-date with what friends are up to on social networking sites. It also looks attractive and the excellent build quality gives you the confidence that it's built to last.

Nokia's software additions to Windows Phone aren't perhaps as deep as we expected -- and the OS is certainly lacking apps in general -- but the Drive navigation and Mix Radio software are definitely neat features to have.

Nevertheless, there are a few downers, including the lack of a front-facing camera, the average quality of the main camera and the fact that, like all other Windows Phone handsets, there's no microSD memory card slot.

Perhaps the biggest issue though is the price. At roughly £400 on pay as you go, it's bordering on the same territory as the Galaxy S2 and iPhone 4S. Both those handsets offer better screens and cameras, and considerably deeper app ecosystems, for a little more money.