What do I need to do to use Phone as Modem services?

If I want to use Phone as Modem service from any cell phone provider, is there any particular model of phone I need. I work at RadioShack so I sell cell phones for a living and I don't know the answer because It's never been a big priority because most customers aren't interested in it. I even called a Verizon store and they couldn't answer. However, now I'm interested in just what I have to do to set it up since I think that may be the most economical way to get internet service when I move. So, any help would be appreciated.