Ok,
So I played with it further (I used InternetCalls for testing btw)...
-Gizmo can call
user@sip.internetcalls.com
-SipBroker can also call
user@sip.internetcalls.com when using EziDial (try here
SIPBroker - EziDial )
-However when registering
user@sip.internetcalls.com and assigning it an alias the call fails when trying to call the alias....
Now granted this looks like a SipBroker related issue.... will try to get Martin, Craig or Tony to take a look...