Tmobile phone with 02 sim?

No you can't use t-mobile phone with o2 sim until you unlock it ...You can easily unlock your phone from t-mobile network lock using network unlock code ...You dont need to take your phone to a shop to unlock it instead you can easily unlock your phone rite from your home using sites like MobileUnlockSolutions.com here they are rendering network unlock code for all mobile models at reliable cost ..You first check that whether the code is available for your mobile model ,country and network provider .If yes then pay for it and unlock your phone then freely use it with o2 or any other GSM sim ...