Will tmobile swap my micro sim to the nano sim for iPhone 5?

Basically I have an iPhone 4 under contract until October 2013, but if I buy an iPhone 5 on pay as you go, will t mobile swap my micro sim to a nano sim whilst I'm under contract?

No reason why they shouldn't as you are still paying the contract. Phone customer services and ask them, you can even order it as it will not become active until you register the new iPhone5 with it in.

You'll be paying extra