How to switch T-Mobile phone service from android to an iPhone?

I've been trying to get a new phone. I've always used an Android and now was thinking about trying an iPhone. Usually with Androids all I have to do is take my current SIM card out of my old phone and put it in the new phone and the service is there and I could use the phone immediately as long as it's with T-Mobile. Would it be the same way for an iPhone? Or would i have to do something extra to be able to get service on the phone. The iPhone is T-Mobile as well.

I believe you have to take it into the T-Mobile store to get it transferred.