voicemail call failed a solution

Been trying for several days to get voicemail to work tried the reset network, called 655 att where they kept resetting my voicemail, send iphone settings with no success. I had switched to att and brought my own number along, got a new sim card in the mail installed it and when long pressing 1 voicemail failed. I had an old alcatel phone so I decided to move the sim card and try voicemail call, it failed but I got a message "no voicemail number on sim" there was an option to add voicemail number to sim, tried the long press 1 and voicemail call completed successfully. moved sim back to iphone and longpress 1, voicemail successfully completed and visual voicemail now works. Hope this post helps someone