Palm info center has an in depth review of the 755p. Most is as you’d expect except for an oddness on the included IM application. If you use IM on your phone a lot you might want to stick to the applications you use on your 700 or 650.
The Sprint model includes a new IM application. It’s actually just a shortcut icon that points you to a free, over the air download. The app supports AOL IM, MSN/Windows Live and Yahoo! Messenger. The Sprint IM app actually charges you by the message, and each message sent goes for the standard sms fee of 15 cents per. If you have an unlimited messaging plan the fee’s aren’t likely to be an issue, without one it can get expensive pretty quickly. Most heavy IM users would be better served with a more economical and feature-full app such as Mundu IM that has a one time upfront fee and no messaging charges.