I agree with you 100% yianniv. Having signal and no service just doesn't add up, but we're here to help. What kind of phone are you using? Can you try turning off the phone, removing/reinserting the SIM then give it another shot after you turn it back on? You should also try scanning for networks to see if you can re-register on T-Mobile's network.
Hey yianniv! Just checking in to see if you were still having trouble with this in your workplace. What kind of phone do you have? Did you have a chance to give Mike's recommendations a shot? Please let us know how you're doing, we'd like to help if we can!