After a call with tech support it has been working for a few weeks (Thanks Voipo).

The solution was to only enter data in the Authentication Name, Authentication Password, Username, Domain (sip.voipwelcome.com), Proxy server port (5061) and Registration server port(5061), Registration refresh time (180) fields.

I am using two VoiPo lines with the phones. The calls are incedibly clear. I am really enjoying the phones and service.