AT&T’s first Windows Mobile 6.5 smartphone, the HTC Pure, has some reasonable heritage; while the casing may look new, the guts of the handset are shared with HTC’s Touch Diamond2. Back when we reviewed the Diamond2 in May, we described it as the best Windows Mobile 6.1 smartphone on the market, and suggested it was well placed for the promised update to 6.5.

The Pure offers a 3.2-inch WVGA restive touchscreen, only now it’s clad in a shiny dark-blue plastic body rather than the metal-edged casing of the Diamond2. What you lose in tactile feel, you gain in a display that feels less recessed than we found the original handset’s to be. Physical controls are limited to a touch-sensitive zoom slider sandwiched between the display and four hardware buttons – call, Windows, back and end – together with volume keys on the top right-hand side and a power/lock button up top. On the base there’s HTC’s usual ExtUSB port (which is compatible with miniUSB) and which – with a frustrating dongle – offers a 3.5mm headphone socket. Like the Diamond2, there’s no way to plug in a standard set of headphones.

Wireless connectivity, meanwhile, includes HSDPA 7.2, WiFi b/g and Bluetooth 2.0, together with GPS, meaning there’s no shortage of ways to get online. A microSD card slot is hidden under the battery cover. HTC’s choice of display is just as bright and vibrant as we remember from the Diamond2, and shows off the latest version of TouchFLO 3D. The company’s own finger-friendly UI sits on top of Windows Mobile 6.5, and works well to keep the stylus in its silo most of the time. For all the details – and opinion – on Microsoft’s new smartphone platform, check out our Windows Mobile 6.5 review. That covers the underlying OS, the Windows Marketplace for Mobile app store – paid downloads from which AT&T subscribers can charge straight to their monthly bill – MyPhone backup and all of Microsoft’s other tweaks and amendments to its Windows Phone platform.

What’s less impressive six months down the line is the performance, especially in the wake of the iPhone 3GS. We found the on-screen keyboard – though well spaced, sensibly laid-out and with decent auto-correction – to be sluggish, especially when typing URLs in either of the Pure’s preinstalled browsers. The Windows Phone has both Internet Explorer Mobile 6 and Opera Mobile, and of the two we prefer Opera’s attempt. While IE Mobile 6 has certainly improved over its deeply disappointing predecessor, and now supports Flash Lite, its rendering abilities fall short; CSS proved particularly tricky for the browser, where Opera Mobile had no problems with the same sites.

The Pure’s camera is the same 5-megapixel autofocus unit as on the Diamond2, offering a digital zoom and touch-autofocus. Picture quality falls short of the advanced optics on recent Samsung and Sony Ericsson devices, but is still reasonable. There’s a minor lag between tapping the display (to take the photo – unfortunately there’s no dedicated camera key), the focus locking and the image being snapped. While the digital zoom is fast, it can’t be used during video recording; however, you can pre-zoom before starting to record a clip.

Battery life is a reasonable two days with moderate use, though if you leave ActiveSync turned on for push-email you may find, like we did, that you need to recharge midway through the second day. As for call quality, the Pure is fair but we missed the particularly clear speakerphone from the Pro2. Given the lack of 3.5mm headphones jack, we found it made more sense using a stereo Bluetooth headset than the awkward adapter dongle (that’s included in the box; HTC and AT&T also provide an ExtUSB stereo headset with microphone). Still, media playback isn’t the Pure’s forte, and neither the Windows Mobile Media Player app nor TouchFLO 3D’s mediaplayer can hold a candle to the iPhone 3GS’s version.

The smartphone space is perhaps one of the fastest evolving in tech right now, and the different landscape in which the AT&T Pure finds itself compared to its Diamond2 sibling is a good example of that. Rival handsets such as the HTC Hero and the iPhone 3GS outclass the Pure’s resistive touchscreen, occasionally laggy keyboard and half-hearted PMP functionality, while the Verizon HTC Imagio offers a bigger display and a standard 3.5mm jack. At $149.99 (following a $50 rebate and assuming a new, two-year contract) the Pure is cheaper than the Imagio, but if Windows Mobile is a must-have we’d plump for the Verizon device.