No, you are looking for someone who is using T-Mobile iPhone 7 Plus on the Straight Talk network that is having problems with Visual Voice Mail. And it is not up for debate, it is long been known that Visual Voice Mail is a CARRIER service. Either the Carrier Settings on your iPhone are not correct for some reason in which case you would need an update from Straight Talk, the APN settings are incorrect if your iPhone is not being shown as supported, in which case you could edit the APN settings but you would need to get the correct settings from Straight Talk, or the is a problem with the provisioning of your iPhone which would have to be corrected by Straight Talk support. Do you see a pattern here? Is there a reason you don't want to go to the Straight Talk forum or talk to their support?
The only user intervention that can be done on an iPhone would be if you are using a non-authorized carrier and then you would be allowed to manually edit the APN. But you would have to get the correct settings from the carrier.
Have you tried restoring your iPhone which would then reload the Carrier Settings? Have you checked the version number of your Carrier settings in Settings > General > About > Carrier Settings and confirmed that is the correct version?
