If you ever change your mind about a call (or entered the wrong number) and pressed "Call", there is NO WAY to cancel the call or hang up. Real phones have that and so should any app that purports to be a phone.
I have some other issues that I'll be reporting on under a different topic -- besides those already been reported by other Beta users.
Looks sexy and all, but doesn't seem to really work that well. Sounds like a secretary that used to work for me a while back...