cell phone as modem for laptop

Hi, I've read a couple postings about this, but I'm still not clear. I wish to use my Sony/E T637 w/bluetooth as a modem for my laptop (w/bluetooth) to access a cheap isp without having to use cingular's pricey data plan. Can anybody give me detailed steps on how to do this? I've managed to dial-up the phone from the laptop via bluetooth dial-up networking, but when the phone lights up and shows the number, it quickly disconnects, and I get a windows #777 error. didn't enter any passwords or login name however, just my home phone # to try it. info appreciated! I wanna get this figured out so I can use the laptop up in the backwoods where theres no wi-fi!