For anyone setting this up in the future.... I used this:

Profile Name: XnetVFX
Phone Number: Phone number without leading 0
Display Name: Phone Number
Authentication Realm: -blank-
Authentication ID: authid
Password: password
Registrar Address: pan.wxnz.net
SIP Proxy: pan.wxnz.net
Outbound Proxy: 0.0.0.0


Registrar Port: 5060
SIP Proxy Port: 5060
Outbound Proxy Port: 5060

Preferred Codec 1: G.711ALaw
Preferred Codec 2: G.711MuLaw
Preferred Codec 3: G.722
Preferred Codec 4: G.729a/b