Following issues this week with calls to SIP2SIM phones not working reliably, the carrier has finally updated their systems to have fixed firewall rules. This solves one of the key issues we have seen with unreliability. Their firewall rules were not properly made from the DNS records for some reason. We are now able to finish updating our routing logic over the next few days. This should not impact services, but there is a risk. Thankfully the risk is quite low, and importantly likely short lived, as it seems their main call handling servers are reasonably quick to pick up DNS changes (unlike their firewall rules). The aim is to make most of the changes over the weekend.
The good news is we have managed to set up a "test endpoint" This means we can test with no disruption to customers. We plan to deploy at a later time when the actual changes needed on the test endpoint has been proved.
More testing on the test endpoint today, slow progress.