We’re running an instance of Asterisk 13.13.1 on CentOS 7.
One of our remote users has reported that he is unable to make international calls on his company-issued desk phone. I can see from SIP debugging that calls end prematurely with “503 Service Unavailable.”
However, I tried dialing a weather number in Australia on my desk phone and the call went through.
Here’s a copy of the affected user’s sip.conf entry along with a sample call log: http://pastebin.com/jqLb39d0