I have iphone 4s use by simple mobile?

My iphone4s was updated yesterday to ios 7, and now my phone can't make calls. I don't know what to do. I need help.
Before my simple mobile was working fine, I can make calls. And now that it updated to ios 7. I can't proceed to make calls.

Call me at 07707925606, dealt with this problem before, I can help you out straight away!