Cell Phone modem via usb cable problem

I have a samsung e 715 cell phone that I want to use as a modem. I hooked it up with a USB cable to my Toshiba laptop but they don't communicate with each other. I spent a few hours with tech support with Samsung and T Mobile but they said it was the cable that is causing it not to work.
Win Xp recognizes the USB when I plug it in and assigns it a com port. The modem is installed to that com port but when you try to connect it doesn't. Gives an error messgae unable to communicate with the modem.
I tried hyperterminal, no connection, AT command failed.
Not that it means that much but the cable is for the phone and it states it is for internet access, downloading ring tones etc. The maker of the cable is Prolific. I e mailed them but so far no answer.
Any suggestions or help is appreciated.

 

Thanks Pete, but I resolved it. It was a bad cable.