Sending back broken Sony Ericsson phone

[_M2]

Currently, I had bought a M600i from craigslist. He told me that the phone part doesnt work but the other functions are good. I tried that Vodaphone mod and switching it to automatic connection, but no help. I searched online for a long time but cant find anything.

If I go to a phone shop, itll cost average $60 to fix it. Should I do this or ask the guy to give me his reciept so I can send it back to SE? Or does anyone know how I can get the phone working again?

ps. the phone is absolutely 10/10 condition and I dont think he dropped it or anything..

When I put my SIM card in, I can log on to the main screen and use the functions but it never finds a provider.. always says searching..