I have a very similar issue. I just got the TX and I have a V3m (razr) with Verizon. This is the configuration I am using:
Phone number: #777
User name: (your 10 digit number)@vzw3g.com
Pass: vzw
I think that's all you need. Basically my phone will usually connect to bluetooth, and it will connect to verizon's internet, but will never stay active more then 10 seconds. As a side note I use these dial up settings with my razr connected to my pc via usb, and it works fine.
So to tim, if you aren't using those settings I listed above, try that first, and let me know what happens. So anyone else, is this a problem with the Tx, the razr or verizon? Thanks