Right when you get a T-mobile phone in the store does the contract start then and there after the purchase?

I'm thinking of getting a T-mobile phone but i wanna take it home first and play with it before i have to use the contract. So does the contract start right when i buy the phone? Or is it when i activate the phone is when the contract starts?|||it's when you activate the phone... but i think you activate it the same day you get it but.. idkk. not sure..|||The contract goes into effect immediately, but they have what is called buyers remorse, if you don't like it you can take it back within 14 days