Would it work if i put a 02 sim card in a T mobile phone?

I am getting a phone that is with T mobile but i have a 02 sim card which i want to put in the t mobile phone but i am not sure whether it would work. Can anyone answer this please.|||no you need to get the phone unlocked on the network go to a phone shop|||Yes - But you have to contact O2 and give them the new phone reg. no. Found inside. That also depends on whether you are on a contract with T-Mobile or not. But there are ways round that. The simplest way to do it is to take it to a mobile phone shop and ask them to help you allow to use the O2 Sim card on the phone. You will be charged a couple of pounds but unless you know what you are doing it is hard to explain the steps you have to go through.