Phone: iPhone 6+, 16GB, Gold, bought midnight day 1, was bought locked to AT&T but paid off and carrier unlocked without a problem. iOS 8.1.3. Network: Apple Airport Extreme 802.11AC, bought just a month ago. Up to date firmware. Now I'm on Tmobile family plan, 2 lines unlimited "Simple Choice". Everything is going swimmingly except wifi calling... As soon as I got home, I factory reset the phone so I could start clean. I updated the carrier settings to 18.1. I enabled "Allow wifi calling" and updated my e911 settings without issue. I then saw "T-Mobile Wifi" at the top of the screen, which indicates I can make calls over wifi. However, putting the phone to sleep for more than a couple minutes seems to lose the "wifi" tag and I am no longer able to make wifi calls. Resetting the phone will regan the wifi tag, but putting the phone to sleep for a couple of minutes will lose the wifi calling feature. I've taken the issue to T-Mobile and they ended up sending me their T-Mobile "CellSpot" router, which is just a rebranded ASUS 802.11AC router. It didn't help. I called T-Mobile again and they said "it's an Apple problem, you'll just have to wait until they fix it with an update". So, does anyone here have the same issue that I'm having with wifi calling?