Unable to make a call

[gemz4the1]

Since the iOS 7.1 update, my phone has randomly been playing up.
Occasionally when I try to make a call, it comes up call failed even though I have a full signal and sometimes a 3G or 4G signal. When this happens my phone doesn't respond whenever I try to call. I press the contact name and it doesn't do anything (usually it launches into a call).
I try switching to airplane mode to reset the signal and double clicking the home button to close the call tab down but it doesn't help.
Any ideas what the problem is?
Has anyone else had this problem?

[MI5]

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@Anonymous wrote:
You could pick up a free sim adapter from any O2 shop which would make the nano sim into a micro/standard sim if that'll make it easier.

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I thought about that but if going to the shop for a sim adaptor you may as well save the extra time and do a sim swap in store......

[gemz4the1]

I did a hard reset and a restore (for another issue) and this problem with the calls seems to have been fixed.  Sorry I haven't identified the problem but hopefully it is a solution for other users.