OK, I was finally able to get the inbound number of a Skype Connect SIP account working and the issue was minor but nevertheless baffled me for a couple of days. I spent many hours, removing and then rebuilding the VoIP Provider profile while playing with Inbound Parameters, the Source ID and the DID field. After a wireshark capture, I finally saw the issue. For the US at least, if you have a Skype Connect account with an inbound number, when you are setting up the account details information, you have to put a 1 in front of the telephone number in the External Number field. Otherwise you will end up getting a 407 error. So for example, in the US you get a Skype Connect inbound number of (987) 555-1212 , you would need to populate the External Number field as 19875551212 . I have seen videos explaining to simply place the Authentication ID in the External Number field but this does not work if you have Skype Connect for outbound as well as a Skype Connect inbound number.