Can i keep my current contract if a purchase a iphone 4s?

I currently have a contract with T-mobile
300mins
300texts
unlimited internet
anyway i'm thinking of purchasing an iphone 4 or 4s so would i be able to cut my simcard into a micro sim and put it straight into a iphone and it will work?

If the phone you propose to buy is sim free, unlocked or T Mobile branded then your (cut down) sim will work. You have to exercise caution when cutting the sim. You could ask your networ to send you a micro sim and request that your existing number is migrated to it. If you choose to do this, remember to back up your sim contacts as the original sim will be deactivated.