Most problems can be traced to the DNS issues. Fongo changed server names recently, and added a new server, without announcing properly. There are 3 servers at the moment: sipnode1.fongo.com, sipnode2.fongo.com, and sipnode3.fongo.com. Old hostnames sip.fongo.com and voip.freephoneline.ca may not be resolved properly anymore by some ATAs. Select one of the sipnodes, and program it as your server. Or better yet, enter the IP address directly. This should solve most of the server registration issues.
PS C:\Users> ping sipnode1.fongo.com
Pinging sipnode1.fongo.com [208.65.240.142] with 32 bytes of data:
Reply from 208.65.240.142: bytes=32 time=13ms TTL=58
Reply from 208.65.240.142: bytes=32 time=16ms TTL=58
PS C:\Users> ping sipnode2.fongo.com
Pinging sipnode2.fongo.com [208.65.240.165] with 32 bytes of data:
Reply from 208.65.240.165: bytes=32 time=15ms TTL=58
Reply from 208.65.240.165: bytes=32 time=16ms TTL=58
PS C:\Users> ping sipnode3.fongo.com
Pinging sipnode3.fongo.com [208.65.240.160] with 32 bytes of data:
Reply from 208.65.240.160: bytes=32 time=16ms TTL=58
Reply from 208.65.240.160: bytes=32 time=16ms TTL=58