T Mobile subscribers receive message "The number is not in service" when placing calls to active AT&T VOIP land line phone number
I just changed with AT&T my landline from hard wire phone line to digital Voice over IP phone line. Using the same phone number, staying with AT&T. I have received several communications from people calling my number saying they are receiving the following message "The number is not in service" But not all callers receive this message. It turns out only subscribers using T Mobile as their mobile phone service provider receive the message "The number is not in service" I've also been told by T Mobile users they receive this message when calling other AT&T digital VOIP numbers. What can be done to fix this problem?