IPhone 4s service not working?

So my dad's old iPhone 4s has been sitting around for a while. My younger siblings updated it to IOS 7. Previously my dad had been using it with a T-Mobile Sim Card, but I don't know if the phone is factory unlocked or not. When I tried to put my own sim card in it the phone said "searching" in the corner, then it said "T-Mobile". It didn't lock up or anything like that. But when I try to text or use Wi-Fi the messages don't go through. Is it because the phone is locked? Or is it something else?

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