I don't think TMo has the 8800 still in stock, some retailers don't. 8800 is full keyboard, the 8100 is not. 8800 has gps built in. Both can take the SD extended memory card.
You need to drop by a retailer and get a feel for the phones in your hand.
The 8800 is only slightly heavier, but is harder to type one-handed (although I can, it is possible, just not as easy).
End of September, around the 24th I believe, the 8300 Curve hits T-Mobile with WiFi. You can get one unlocked now and change the operating system to the one from British carrier O2 so it will work with T-Mobile. That's what I'm using right now and it's pretty spiffing if I do say so myself. :D I highly recommend fondling one before purchase. Nothing like getting the feel of it to know if you're comfortable with it or if you need to look some more.
WOW!!!WOW!! A lot of information here!! Thank you guys.. You guys are awesome I can wait a few weeks ....... i might get the new one. Im gonna keep checking the forums I have a lot of reading to do. BB rocks!!