Cell phone as modem

OK a couple days ago, I bought SnapDialer and a data cable that would allow me to hook up my Samsung A660 Sprint PCS phone to this laptop I'm being forced to use over the summer. It worked fine at first, but then just started freezing the whole computer up whenever I dialed in and then started using any Internet program. If I used the regular modem to dial, there was no freezing.

I uninstalled/reinstalled the USB driver and the SnapDialer, but this did no good. I updated to the newer USB driver, but this did no good either.

I then read on other message boards that using your cell phone as a modem in this manner can get you in trouble with the carrier and even get your account terminated. Why is this? Why should Sprint care if I use my phone as a modem?

 

It is using their Internet service. It's using the phone's Vision browser to dial onto the PCS network #777 and then logging in with my user name and PW.