Facetime Errors on iPhone

When my wife and I first got our iPhones 4s's they were very reliable when placing facetime calls between to the two phones and to our son who has an iPod Touch. We've notically lately that most attemps results in "FaceTime Failed" Dave is not availabe for FaceTime. The example just given is when I'm calling her and her phone is ringing but when attempting to pick up on the receving phone the dialog indicates that I'm not available.

At first I though perhaps my carrier was placing restrictions so inquired, not the case. When I turn off using celluler networks I get the same results. Any ideas? I tired getting answers from my carrier and they were clueless. Thanks for any ideas one might give.