Can you please provide a little more detail. For voicemail set up on my iPhone SE, I ihad to initially switch/set Cellular data to ON. Once setup I can switch cellular data to OFF and voicemail works OK. It would be great if you can please update this post with your solution. Thanks.
"Cellular data has to be turned on and left on in order for voicemail to work on my SE" - You are right. For Voicemail notification and visual voice mail to work, cellular data needs to be ON. If Cellular data is OFF caller is able to leave a voice mail message which can be retrieved by dialing voice mail.
I would love to know why xfinity mobile customer service doesn't know what the customers that post on this forum know. Over the last 2 weeks, we have called customer service 3 times about my son's voicemail, with each call lasting about an hour. Every time they have told us a story about how there was a change in their voicemail system and some people are having problems. They would write a ticket to escalate, but we should call back in a few days if we're having problems and it will be fixed. They NEVER suggested that we check this setting in the new iphone. Today was the third and thankfully final call, when we got the same story, When my husband told them that we were frustrated, and concerned (son's leaving for school soon), they suggested that we return our phones and terminate their service. WHAT?!?!? Then I found this forum. The entire problem was solved in 10 seconds. If you can't set up or access voicemail, check the settings on your phone to make sure that cellular data is enabled.