Apparently AT&T isn't too happy about you using Skype on devices on its network, so the limitation has been built-in ether by HTC on AT&T request or later on by AT&T itself and the limitation is this :
Skype mobile software can't use built-in speaker & microphone (hard to swallow) BUT ALSO bluetooth headset !!
AT&T Tilt uses HTC ExtUSB connector - HTC propitiatory connector for data/voice and power.
Its also backwards compatible with standard mini-USB plug. It looks like there are 3rd party ExtUSB to 2.5mm and 3.5mm headset adapters. More updates to follow....
Update: A friend of mine, recent owner of TyTN II wrote a good review: http://www.governmentsecurity.org/forum/index.php?showtopic=28155
