Achieving the right balance between size and functionality has long been the challenge with smartphones. O2 has just about got that balance right with the Xda II Mini, providing all the features of a tri-band smartphone packed into a case only slight larger than a mobile phone.

The Xda II Mini is light, compact and fits comfortably in the hand. Unlike the larger smartphones, such as the HP iPAQ or O2 Xda IIs, the Xda II Mini can also slide comfortably into a pocket, making size a big selling point of this phone. Looks are another bonus, with the sturdy attractive silver casing and large LCD screen.

O2 has outfitted the Mini with an Intel PXA272 416MHz processor–the fastest processor on an O2 device with the exception of the just released Xda IIi. The Xda II Mini runs on Microsoft Windows Mobile 2003 Pocket PC Phone Second Edition and applications like Word, Excel, Outlook, Internet Explorer, PowerPoint and Windows Media Player 10 are all provided.

Unlike its larger cousins, the Mini only comes with 64MB of onboard memory, but an MMC/SDIO card slot is provided at the top of the phone for an extra memory card.

O2 has managed to integrate a large 2.8″ TFT LCD 64,000 colour display, but does not have a keypad on the phone. An on-screen keypad is displayed when using the phone, but they keys are small and some users will have to dial numbers with the stylus. The large and sharp screen which dominates the device is impressive – the screen also lets you view files in portrait and landscape mode, with the icon to switch views conveniently located at the bottom of each screen.

As popular as the device was with executives and the so call ‘geek’ user base, one common gripe was its size. Despite the many adverts promoting the device as a pocket friendly gadget, the hard reality was its size was anything but pocket friendly. Not even the successor to the original XDA, the XDA II could parade size as a selling point, as both weigh about 190g and have roughly the same bulky physique as a fully endowed Pocket PC. Naturally, size reduction is the next step in the XDA’s evolution and hence the birth of O2′s latest offering – XDA II mini. It is hoped that with this new product, the company can finally win over the hearts of consumers outside the executive and geek user group.

The first thing that catches the eye is, well, the Xda II mini’s tiny form factor, particularly when placed next to its heftier sibling, the Xda IIs. According to O2, the Xda II mini is about two-thirds the size of the Xda II and weighs just 150g, making it a far more portable PDA-phone for frequent travelers. The matt silver-white finishing on the exterior adds to the overall clean and comfortable touch and feel, although our first impression is that the mini somewhat lacks the design elegance of the earlier Xda offerings. Impressively, O2 manages to equip the Xda II mini with a faster 416MHz processor than the Xda IIs. The tradeoff is a cutback on the onboard memory size to 64MB RAM and 64MB ROM, although O2 makes up for this with a free 256MB SD memory card bundled in the standard package. This will certainly come in handy for storing images snapped by the built-in 1.3-megapixel CMOS camera, again an improvement over the Xda IIs and Xda II’s VGA-capable shooters. Downside: The Xda II mini comes with all the standard connectivity options such as Bluetooth, infrared, triband GSM/GPRS and USB (through the mini USB port). What’s missing, however, is built-in Wi-Fi which will probably disappoint avid hotspotters. Although users can still connect to a wireless network via an optional WLAN card, it will mean that the MMC/SDIO expansion slot cannot be used for other purposes. One of the tradeoffs for the reduced form factor of the Xda II mini is its smaller 2.8-inch TFT touchscreen. Even though it offers the same 320 x 240-resolution and 65K-colour depth as its Xda IIs predecessor, the result is smaller fonts which can be quite an eye strain for some.

Simply put, the O2 Xda II mini, or mini for short, looks gorgeous. The seductive silver finish surrounded by a matt black-ridged circumference give the device a refined and classy image without being too flashy. Users who previously hesitated over the O2 Xda IIs and the HP iPaq h6365 because of their bulk shouldn’t have the same issue with the mini. At 58 x 108 x 18.1mm, the form factor befits that of a true pocket-friendly PDA-phone which also fits comfortably in your palm. You can also carry the mini on your belt using the supplied leather case. Although some may lament the 150g weight, the mini is considerably lighter than the Xda IIs and only slightly heavier than the PalmOne Tungsten T5 which doesn’t have phone capabilities. The usual solid construction and excellent build quality of an O2 product can also be found on the mini.

Using a 2.8-inch touch screen, the 240 x 320-pixel resolution display puts the mini on par with the Xda IIs and HP’s iPaq h6365, though both deploy larger 3.5-inch TFTs. The 65K-color screen looks excellent with sharp contrast and can be clearly viewed even under direct sunlight.

Forgoing an external QWERTY, four soft keys–two for phone functions, another two for contact list and calendar–as well as a five-way navigation pad grace the front panel. Additional shortcut keys for notes, camera, volume and power are located on the sides of the mini with the infrared port on the lower right. While the stylus is inconspicuously concealed on the right, it is too thin for a comfortable grip.