I found a iPhone 4 but it won't get any signal?

Basically my friend works in a tea room and one day they found this iPhone so they didn't give it to me straight away they held it for 3 months to see if the owner come to claim it but they never returned so I got the phone so now when my sim is in it I don't get any signal it dosnt say no service it just don't have any bars but I can iMessage and go on App Store and stuff anyone know why I won't get any signal and if so do they know how I can get it to work thanks guys:)

If the person had "find my phone" turned on, they can remotely disable it. If you took it to an iphone or ATT store, they would be able to tell it wasn't yours by the IMEI thingy.

The iphone 4 had a massive problem with signal you should be able to get a case that fixes the problem. Check with apple

you can't just put any SIM card in a iPhone and the reason there is no signal is because the phone is locked and doesn't have a service provider because if the person was smart and apparently he was he disabled his phone so people couldn't burn up his credit card with wifi and apps

I think it might fix itself if you connect it to itunes and return it to factory setting, that way it's like nothing ever happened

I'm going to suggest removing your sim and sell it as you will get a fair bit of money from it, then buy yourself another one that works