3. The Keyboard Is Mightier Than The Pen

Many PDA phones have touch screens and an increasing number of devices have QWERTY keyboards, too. Blackberry devices don't have a touch screen because they have always had a QWERTY keyboard and a jog dial. The Motorola Q, Samsung BlackJack (the i600 in the UK) and T-Mobile Dash (the HTC Excalibur) have QWERTY keyboards and no touch screen because they run the Windows Mobile Smartphone OS, which was designed for phones with a numeric keypad and doesn't support touch screens. It has fewer features as well; you can view Office documents but not edit them, for example.

Some Windows Mobile Pocket PC Phone Edition devices - like the HTC Artemis, the Asus P525, the Mio A701 and the i-mate Jam -only have the touch screen and often resemble the original iPAQ. Others-like the HP Mobile Messenger, T-Mobile MDA, Palm 700w and HTC Universal and HTC Tytan - have a touch screen and a QWERTY keyboard. Sometimes this is underneath the screen like a Blackberry; sometimes it folds, slides or swivels out from beneath the screen. You can still navigate with a pen although arrow keys, soft keys for the menus and an OK button mean you can do everything from the keyboard as well.

Some Symbian PDA phones have touch screens, like the Sony Ericsson P990, which has a numeric keypad as well. Others, like the Nokia E62, have a QWERTY keyboard and two or more soft buttons plus a joystick or four-way controller. A full keyboard lets you input text significantly faster than writing individual characters or tapping them out on an on-screen keyboard and it's more accurate than handwriting recognition. Check the size, shape and spacing of the keyboard though; the keys on the E62 are close together and hard to press while the square keys of a Treo can make it too easy to hit the wrong key. Very small keys are usually uncomfortable, too. The slightly angled keys on a Blackberry give you a good target to aim for and enough space not to hit two keys at once.

Usually you'll type with thumbs rather than fingers so make sure you can get a good grip on the case and check the balance; you don't want the device tipping out of your hands as you type. Also check which punctuation keys are available from a single keypress and which you have to access via a function key: the full stop is on its own key on many Windows Mobile devices, but the Blackberry keyboard puts it in automatically when you type two spaces and gives you a symbol key for advanced punctuation instead.

Devices that have either a touch screen or a QWERTY keyboard but not both are the smallest and lightest devices because there's simply less to fit into the case. Unless you're actually typing or writing on screen - when you'll need both hands or at least both thumbs - you'll be able to use a PDA phone with one hand providing you can actually fit your hand all the way around it. A jog wheel and dedicated buttons on the side certainly help with that but a joystick or four-way controller helps here. The HTC Tytan has both a jog wheel and a trackball at the base of the screen, giving you scroll or zoom plus cursor control.

Touch screens don't make a significant difference to the quality of what you see on the screen but they do make it harder to read the screen in bright sunlight unless you have a transflective screen like the Mobile Messenger. A few devices like the Blackberry 8700c and the Nokia E62 have an ambient light sensor that dims the screen indoors to save power and brightens it for readability outdoors.

Screen sizes vary-usually between 2" and 3" -but resolution makes a difference too. The typical Windows Mobile screen has a resolution of 640 by 480; the same as a VGA monitor but in a much smaller area. Palm screens are 320 by 320 - although the 700w is only 240 by 240 as is the HP Mobile Messenger, which can cause problems for some applications because you can't see the whole window on screen and some refuse to install because of this. The Nokia E62 is 320 by 240; the same quarter-VGA resolution as the Motorola Q and Samsung BlackJack.

Whether it's a big screen or a smaller screen and a keyboard, the real estate adds up. You couldn't mistake a PDA phone for a standard phone; these are family-sized candy bars. If you find these devices just too bulky to hold up to your ear, try using a headset (wired or Bluetooth).

You could mistake the specifications for a phone, though. Treos and Windows Mobile devices have voice dialing, speakerphone, vibrate mode, conference calling, Bluetooth and polyphonic or MP3 ring tones. The Treo 700w has an excellent voice mail interface that replaces cumbersome number menus with VCR-style controls. Both Palm and Windows Mobile Treo models let you send a text to explain why you can't answer the phone right away. Windows Mobile phones always have dedicated volume controls. Symbian and Blackberry devices have a similar set of phone features. Windows Mobile is currently the only platform for which Skype is widely available (there is a Symbian Skype tool from iSkoot, but it's only available on X-Series phones from 3 in the UK).