I've been using a factory unlocked iPhone on TMO for about 1 year and recently my voice mail (VM) stopped working in that 1) I would not receive an alert advising me of a new VM and 2) it would not show a badge on the phone icon showing me the number of VM's that existed. When this happened, I noticed that when I went to the phone icon and pressed the VM option that I had the Visual Voice Mail (VMM) screen. Previously, when I had a new VM and went to the phone app and pressed the VM button it would automatically dial VM and I could access my VM's. If I rebooted my iPhone, it would work correctly for the 1st VM which would use the basic VM but then "turn on" the Visual Voice Mail for subsequent calls. Visual Voice Mail also allows you to record a greeting and change your PIN (in the phone section of settings) but when I tried to do either of these it failed (permanent spinning wheel).
I contacted TMO support asking them turn off Visual Voice Mail and they said no problem and reset my voice mail options (I had to re-enter my pin and setup my greeting). After they did this my voice mail started working fine using the old style, basic VM procedure. However, the TMO rep said that my Visual Voice Mail had not been turned on so he couldn't turn it off. Something that was done when he reset my VM did clear up the problem but I don't know what. I verified that the "fix" continued to work after a reboot of my iPhone.
Anyone else have this problem?