Has anyone had success using Zoiper on an iPhone 4S over OpenVFX?

Get a "Registration Failed. Connection Error 3, unknown" message using the following settings:

Account Name: VFX
Domain: pan.wxnz.net
User Name: [from "username" field in provisioning email "C3NDXxxxxxxxxxxxxx"]
Password: [from "secret" field in provisioning email "sldkjfxxxxxxxxxxxxxxxxx"]
Caller ID: 
Auth Username (advanced settings): [from "username" field in provisioning email "C3NDXxxxxxxxxxxxxx"]
Outbound Proxy:disabled

WXC help desk say they can see the soft phone attempting to register but with incorrect authentication details - but they can't tell me what they are.

I successfully use the Mac soft phone called Telephone with the same account settings (shutdown when trying to register Zoiper on the iPhone so only one registration attempt at a time).

Any suggestions greatly appreciated.

Cheers