FREE tethering question?

alright, so i am on a normal voice & text plan under Sprint. we pay way too much a month, so i'm hoping this might work to redeem that cost.

i am wondering how to tether (i know you can't at high speeds without a plan!) at speeds as fast as a telephone will allow. we aren't paying for data or any of that.

i have signed up with MetConnect, a free dial-up ISP for the NY area. i am a user now, and i have the connection phone number(s).

now, when i plug my phone (motorazr v3m, Sprint) into my computer upstairs, it says "MOTOROLA USB MODEM." can this be used just as a normal phone line modem??? as in, can the connection number simply be dialed, using nothing but minutes? (i have free nights and weekends.)

all i want to do is to be able to use AIM. i don't think this uses enough bandwidth to trip any suspicion with Sprint, and i don't think it should, if i'm using a dial-up, minimum amt of bandwidth.

any help would be great; just want to make sure i won't rack up fees. thanks!