Right now I'm on Alaska Airlines with a Verizon iPhone 6S iOS 10.1. Used my T-Mo 200MB iPad # to login.. working like a champ. My phone is in airplane mode, says VZW Wi-Fi on screen.

I'll try this configuration in a few weeks when I fly AA. My friend will be with me, she's AT&T, same device and OS.

After my 1 hr session promptly ended on Alaska, I had the option to keep texting only or buy more data. When going back to purchase screen, the T-Mo option was updated to "check-in"

From there I pulled out a spare iPhone (Verizon iPhone 5, iOS 8.4), was able to login with same (T-Mo 200MB) credentials, got another hour of service on another device.