T-Mobile is a phone company.
You can get a T-Mobile phone, unlock it & use it for a different cell phone provider (like Sprint).
The thing is, I don't know if you can do Sprint 'cause you have to have a SIM card. The only provider I know that uses a SIM card is T-Mobile & AT&T/Cingular, but maybe more providers use SIM cards than when I last checked/heard.