I have a question about cell phones.?

I wanted to know it if was possible to have a t mobile phone (htc G2) and put another sim card in it for another cell phone company like boost, or sprint, or At &t and have my monthly bill through one of those companys. I love my phone. I am just getting tired of t mobile and I don't feel like I should have to buy a new phone since I just brought this phone a few months ago..