Hi,
Looks like Axon PBX is dropping the end part of the SIP address ";user=phone" and leaving off the final ">" See bolded SIP addresses below.
06:18:12 UDP Packet Sent to 72.5.80.116:5060 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
ACK sip:72.5.80.116 SIP/2.0
Via: SIP/2.0/UDP xxx.xxx.78.148:5060;rport;branch=z9hG4bK423208
To: "1234567890" <sip:1234567890@72.5.80.113:5060;user=phone>;tag=GR52RWG346-34
From: "xxxxxxxxxx@i2telecom.com" <sip:xxxxxxxxxx@i2telecom.com:40893>;tag=7757
Call-ID: 618132008-83465E0518192906301@72.5.80.113
CSeq: 340 ACK
Max-Forwards: 20
User-Agent: NCH Swift Sound Axon Virtual PBX 2.00
Route: <sip:72.5.80.113:5060>
Authorization: Digest username="xxxxxxxxxx",realm="72.5.80.113",nonce="F71D13EE5277BEC0304A83024AB824F0",uri="sip:72.5.80.116",response="d8b840a3755a5f8de4e7d8b05b7bbe98",opaque="2BCC2DB101990D646A20ECB43326C8DA",algorithm=MD5
Content-Length: 0
----------------------------------------------------------------
06:18:12 UDP Packet Sent to 192.168.1.8:18152 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
INVITE sip:101@192.168.1.8:18152;rinstance=20d8b85696b4b9ab SIP/2.0
Via: SIP/2.0/UDP 192.168.1.3:5060;rport;branch=z9hG4bK433208
To: <sip:101@pbx.domain.com>
From: "1234567890" <sip:1234567890@72.5.80.113:5060;tag=7759 <----Missing end bracket
Call-ID: 1214733862-3208-pbx@xxx.xxx.78.148
CSeq: 953 INVITE
Max-Forwards: 20
User-Agent: NCH Swift Sound Axon Virtual PBX 2.00
Contact: <sip:101@192.168.1.3:5060>
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, INFO, REFER, NOTIFY
Supported: replaces
Content-Length: 0