I have "Acrobits Softphone" on two iPhones. One stays in network and connects over Wifi and works fine. The Second connects over 3G as an External Extension. The device registers but when I go to call another extension that is on the internal network of the PBX it fails the call right away and gives the following 2 errors in the Server Activity Log. 19:34:08.021 [CM502001]: Source info: From: "First Last"<sip:email@example.com>;tag=F9DA963FC88DC83FE493E33D25476A14<sip:firstname.lastname@example.org> 19:34:08.020 [CM503013]: Call(1): Incoming call rejected, caller is unknown; msg=SipReq: INVITE email@example.com tid=Ytf1gBNA4YKWCMNn cseq=INVITE firstname.lastname@example.org:5060 / 2 from(wire) xxx.xxx.xxx.xxx is my external IP ooo.ooo.ooo.ooo is the external IP of my iPhone Extension 101 is the iPhone and 100 is the Softphone inside the PBX's network I may be overlooking something obvious, but ... what am i doing worng?