As of 12/08, according to TalkSwitch technical support, despite the fact that the SIP RFC describes both the username and auth. username as alpha-numeric, the TalkSwitch server does not allow for a alpha-numeric username. They only allow for a numeric username.
OnSIP uses the SIP protocol as defined in RFC 3261.
OnSIP treats all numbers as either extensions or phone numbers. Therefore, we cannot have usernames that are only numeric. All usernames and auth. usernames are fully alpha-numeric.
We would therefore recommend a more SIP compliant software PBX like Asterisk and cannot recommend TalkSwitch to our customers at this time.