Strengths and weaknesses:

iphone:

Strengths:

- Best keyboard on a device of this size.

- Tough, scratch resistant screen.

- iPhone switches back automatically to the task you were working on when a call is finished

- Easy conferencing (up to five people, switch in and out of calls at any time).

- Fun and useful visual effects and transitions.

Weaknesses:

- No cut and paste.                                                                        

- No native 3rd party applications.

- No document editing.

- No voice-dialing.

- No speed-dial.

Blackberry

Strengths:

- It's highly secure.

-  It integrates well with other platforms.

- It works with several carriers, and it can be deployed globally.

- It is easy to manage, has a longer than usual battery life.

-  has a small form-factor with an easy-to-use keyboard.

Weakness:

- Hang Working system is very similar to BlackBerry PC performance. Applications that use the BlackBerry will reduce backup   memory thus slowing down system performance. Distinctive characteristic is the frequent appear-hour spin on the screen. Most powerful solution is to take off the battery.

- Problem in virtual networks such as Bluetooth, Wi-Fi, and GPS.
- Unstable BlackBerry Messenger connection.

- Email is often absent.

- Trackball.

Windows mobile

Strengths:

- Almost as flexible as Android and almost as elegant as iPhone.

- Hopes for Windows Mobile 7

- Hopes for Zune HD Phone

Weaknesses:

- Hardware still have a lot to improve, HTC HD2 isn’t enough.

- Marketplace still needs some developing to do.

- OS still need more work

- Hideous UI, severe hardware limitations, not as open as android.

- very few APIs open to developers, limited app market by comparison to the other two, "very locked down" in most people’s opinions, not much room for customization