The VoLTE thing is very annoying. From my conversation with a high level support tech, VoLTE is MANUALLY enabled on all femtocells. So after a reset or initial power up, it goes into a queue, and some engineer or support person starts going through the queue and toggling it on if certain conditions are met. I've had it take as little as 3 days, and as long as 2.5 weeks. It's pretty shocking that they don't have a better way to do this.... My guess is it's something to do with integration into the nearby network, so that macro handoffs are smooth. I've heard that after initially getting enabled on a femto, that future enablings are much faster (1 day or so), but I have mine on battery backups and don't really want to test it... You'd still think that they'd be able to automate this though... Until a couple months ago, only LTE relay magic boxes got VoLTE. Anything using wired or wifi backhaul didn't. When I reached out to the above tech about this, he said it should work, and then 3 days later I got it enabled. Either he fixed the bug, or it was incredibly coincidental, after many months of not having VoLTE enabled.
Well I guess it isn't actually roaming anymore even if it shows as such as TMobile coverage is now native coverage provided your phone has the necessary bands to latch onto whatever technology those particular towers are broadcasting.