Thank you for making this thread...you beat me to it. Same exact issue here. I was in touch with a T-Mo tech today and after several tries resetting my VM and "reprovisioning" (?) it, she put me on hold and talked to her supervisor. What I was told is that everything is set up correctly on their end and I just need to wait for Google to update the phone app (or send feedback to them). I was told it's a "known issue" with the P8/8pro. I can "dial in" to hear a VM or see it by using the T-Mo VVM app, but the tab on the G phone app for VM still says "can't activate." Annoying but not the end of the world.