When users dial out to AT&T subscriber numbers they are experiencing issues with delayed or no ringing heard at the dialing station, if it rings the call may connect or may not, if it doesn’t ring, the call shows it is connecting. I have draced the issue to the fact that I pass DIDs that I have assigned to a PRI from the local TeleCo as the outbound CID. I pass these numbers as CIDs because those local DIDs are assigned to my inbound routes, which is where I need people to call me back. I have no issues when dialing cell phones on other subscibers such as Verizon, T-Mobile, Google, etc..
I have spent hours online the phone with AT&T, who will only discuss this from a subscriber, focused only on their specific assigned number. I have also had several open tickets with the SIP Service provider who had me test by assigning one of their numbers to the CID and everything functions fine.
You need to talk to your actual teleco that you connect with. They are the ones that route the calls to the destinations like ATT. You need to find out why your calls aren’t being routed properly. It’s a carrier-carrier issue and it’s not something you can resolve by calling AT&T.
Assuming they provide such a service, you will need to prove to your ITSP that you control the numbers you are trying to present. This is a measure against vishing and it should not be possible to circumvent it within FreePBX. If they don’t allow you to white list the numbers, you will need to find another provider.
We had the exact same problem with T-Mobile for over 2 years.
Turned out our SIP provider made requirement changes and never notified us. If you are dialing in the USA now, most calls are expected to match 2 things. 1) the outbound caller ID must match the phone numbers assigned to you and 2) that outbound caller ID and the number you are dialing must include the +1 for the country code to be fully E.164 compliant
“VoIP and SIP routing, numbers must be formatted in the E.164 global standard, which strictly requires the +1 country code for the U.S., even for domestic or local calls”
Check and see if that is part of the issue ?
Another problem we had with T-Mobile is they introduced a new “spam” pre filtering feature and I think it was too aggressive for numbers it did not recognize. It would basically kill the call and tell us to chek the number again.