We have a customer with a SV8100 with a PRI that can't call out on certain channels but it keeps changing. They will call one day and not be able to out on channel 23. We put channel 23 in a different trunk group and they will call again and say that now they can't call out on channel 21. They get a busy signal even if the line isn't busy. We upgraded the software to 11 last week but it's still happening. The carrier says its not them. It's been installed for years and this just started happening.