Get a PPC 6700 from Sprint. I use it VPN; access IB's mobile trader and Metatrader's mobile app. I average 600kb in town. The only caveat would be the need for the occasional soft-reset.
I have an older Treo 600 and its okay for checking my positions while on the road using IB's MobileTrader. Its a pretty slow though.
Is the data transmission secure or anyone with some technical knowlege can take a peek at your account?