I recently purchased a Treo 600 for T-Mobile. I had been using a Microsoft powered Smartphone but had found it had limited features and would not sync with my Act! contact management software.
I am hooked! I am already planning to upgrade to the new Treo 650 when they come out for T-Mobile. It does absolutely everything. I have third party software, Chatter, that automatically pushes email to my phone using an IMAP connection. I can send email and SMS text messages easily because of the Qwerty keyboard.
It also has a calendar (which syncs with Act!), address book, voice recorder, digital camera, MP3 player and more. I even found a third part SSH app so I can administer my servers from the GPRS internet connection on the phone.
I was originally skeptical about it because I thought the size might make me feel like I was holding a PDA up to my ear instead of a phone, but the Treo is very small and light so it feels very much like a phone and not a PDA.
If you need a phone and Palm powered device, get the Treo. You’ll be surprised how much more productive you will be.