I have the treo 750 and love it. It is a PDA and phone. Only downside is that the phone speaker is a bit ahrd to hear, but I am used to it now, and on speaker it is fine.
I have epocrates, stedmans dictionary, med calc, pregnancy calc, immunization schedules, etc etc on there. No problem getting all the med software. Plus it has the standard calendar, memo, to do list, alarm clock, etc.
It takes pictures, has a video player and has web access, so I am happy.
I suggest getitng a sizeable SD card for it and looking into providers for the phone/internet part. Some are much more $$ for internet and messaging.
If you have more specific questions and don't get them answered through search, feel free to PM me. also check out mytreo.net