Hi guys, as I reported on May 17th and June 4th I was faced with some connection problems of iMessage and facetime. In the mean time my friend and I checked facetime and iMessage after updating both iPads to iOS 6. Result: Both apps work as they should! This is the proof to me that it was an Apple issue and not a WLAN router one.
One note regarding the quality of facetime in comparison with skype: Forget skype, the video quality is much less than the one with facetime!
Stay tuned! 😉