If your voicemail app will not work after changing carriers...you can try the "solution" in "VM app not working" in the forum. But if it still doesn't work here is the awful solution. I switched 50 lines over from Verizon to AT&T and found that in all the Samsung phones the voicemail would not work and clearing cache and data did nothing to solve the problem. The issue arose with the privacy settings that Samsung offers/offered at the time...if you do/did not allow the call logs to be accessed by Samsung during initial setup...when you switched carriers you can't/couldn't change that setting after the first time you set up that phone. If you went into the app settings you couldn't give access to call logs. It just failed and went back to the original setting. The only solution to this that I could find is to factory reset the phone...make sure Samsung had access to "call logs" during initial setup and then everything worked fine. I verified this on multiple phones (S22's or S22+'s) that were switched over from Verizon to AT&T. I suspect that it is the same problem regardless of carrier or direction of switch based upon my interaction with reps from all 3 companies. My AT&T rep sent this along to Verizon and Samsung but on any phones that were setup that way originally; the voicemail will fail unless Samsung releases a patch and fixes the underlying problem.