I had this issue for ages and I could not make/receive calls etc. I tried everything and then I did the System Restore thing and cleared the cache and did a system reboot and everything is perfect now. I think this limited service thing is a common problem and the solution I found was not directly related to this particular issue but I thought I would try it anyway as the phone 'system restore' did not rectify the issue. I hope this info helps someone else out.
(Switch phone off, press and hold down the 'volume down' key and at the same time press the power on key on top of phone, choose 'System Restore' (volume up and down will navigate the menus and power key will select option) when I selected 'System Restore' a pic of phone appeared and a red triangle with exclamation mark, after a short while it will enter a menu and from there I chose clear cache and system reboot. Good luck