Galaxy Ace Can't Make Or Receive Calls

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http://forum.xda-developers.com – My phone won't allow any outgoing or incoming calls calls. I have full coverage and when I dial it straight away goes "Call Ended" Then when someone tries to call me they get a call rejected. It can send and receive texts fine. I recently rooted the phone to unlock it, then unrooted. The problems began then. Also I should note while rooting it set the phones IMEI to a bunch of zeros in case that makes a diff. I just flashed the phone to stock 2.3.6 a while ago in the hope it would fix but no luck. Any ideas? (HowTos)