Same problem with mine, needs multiple attempts to call anyone, just keeps locking up. Almost unusable, was ok on the 4s
I've been using mine on a daily basis and not having any problem.I'm running 4.1.1310
Only problem I've been experiencing is a purple line at the bottom of my video and a random green dot and I think that is because of a skype bug not a problem with my device.
The Skype app has just been updated to v4.1.1, adding support for iOS 6 and the iPhone 5.