Hey,
That's my FAQ -- I wrote that HOWTO for using a BlackBerry as a modem for laptop.
My experience is:
7290 -- about 40 Kbps (GPRS)
8700 -- about 150-200 Kbps (EDGE)
Curve 8310 -- about 150-200 Kbps (EDGE)
Bold 9000 -- about 1200 Kbps (3G -- broadband on a BlackBerry!!!!!)
I love the Bold, because its 3G means I get broadband instead of dialup. But for TMobile you may find it easier to stick with EDGE. But you can get an old 8700 on eBay for $50, move your T-Mobile SIM card from the slot behind your battery in your 7290 (you don't even need to call T-Mobile or let them know), plug the SIM card into your 8700, and you're on a much better BlackBerry with faster Internet, similiar to "Highspeed Lite" speeds. The SIM card looks like a memory card. To transfer your setup, Click Email Settings icon, transfer your email address. Use BlackBerry Desktop to transfer your addressbook/calendar/etc. Then you've switched BlackBerries on a no-contract basis!