SIP2.0 401 Unauthorized response when dial 7777 to Asterisk

sip 7777 7777 is hard coded into the software. My workaround is an outbound rule to 'fix' 777 dialled from a phone to 7777 down a specific SIP trunk.. I have a problem I am using voicepluse for my SIP service I have 2 numbers one is for voice and the other for fax. There was a problem on their end

siput 303 slot, When I call from a GSM cell phone, my TG100 GSM gateway answers and dials extension 7777 to server, Extra 10% Off + Free Shipping on Your First App Purchase |.