My wife and i both have BB Pearls - mine for work, hers for personal use.
1) Mine is integrated with our corporate Exchange email system and gives me exactly what I need - email, calendaring and contacts.
2) My wife uses her phone for yahoo email access, text messaging, MMS (picture) mail and is quite happy with it - she upgraded from a Razr.
3) Web Access - ok for getting specific info such as sports scores, weather, movies. Not worth a darn for browsing.
4) We both use ATT - i'm happy with the service and rate plan. That said, i get a pretty good discount through my company.
5) To access email and access the WWW, you'll need a data plan. I went with an unlimited plan (29.99 + voice plan)
6) Depending on your tech skills and patience, configuring a BB for email access and other web features can be a bit trying. Try to find a dealer who can help you out.
7) Here is a great BB forum http://www.pinstack.com/
In regards to the IPhone
1) Wait for the 3g version - access over ATT's edge network is (according to reports) fair to unusable.
2) If you really want to stay with TM (or hate ATT), there are rumors about Apple releasing an unlocked version sometimes this year.