I use a 650 on Cingular. Don't want to clutter your life with more forums (nor do I want to divert your attention from CJ's personal blog ), but take a look at the Discussion on TreoCentral. It is the X5World of all things Treo.

With that out of the way, I use few apps for fear of mucking up an already unstable OS. I use VeriChat for my IM needs (awesome app), ZLauncher, TakePhone, and Backupbuddy. These are all popular apps with demo trial periods (I paid for VeriChat, going to pay for the others soon), and all have been talked to death on the forums.

Enjoy your new toy. I love mine.

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-'13 E93 M3 Cab, Interlagos Blue, Carbon Black leather, DCT, all options, and fun, endless fun!
-'13 X5 35i M-Sport, Carbon Black & Cinnamon, Dinan Stage 2!
-'15 Toyota Sienna Limited Premium AWD, Silver & Grey, Nav & BluRay, and less lame than the 2011 it replaced
-'07 Mini Cab S, Laser Blue, 6sp, endless fun that ended (sold)
-'04 X5 4.4i, loaded, loved, modded and sold