One million Sprint customers to supposedly be transitioned to T-mobile network on June 15. I don't know if or how Sprint MVNOs are involved in this transition and who will be one of the lucky ones. My Sprint service greatly improved a few months ago, so not a big deal to me.
"This pinpoints June 15 as the start of the program's "second phase", which will give approximately one million Sprint subscribers the opportunity to get an early taste of the future."
Guess I'd better keep my trusty old flip phone (on a very elderly grandfathered T-Mo plan) handy, and maybe also my FreeUP phone for backup, just in case my main phone temporarily loses service in the transition.
Thanks for the heads-up. Should make for an interesting start to the week ahead!
So it's the 15th or big transition day for T Mobile, and it appears it's an unlucky outage day for some customers. "There's something happening here
What it is ain't exactly clear"
To that I'd say:
"Stop children, what's that sound?
Everybody look, T-Mobile's down."
And oddly enough, my trusty main (Sprint MVNO-based) phone is working just fine so far today. Go figure.
The adventure continues...
Say it aint so! The new T-Mobile is too big to fail!
Still down.
Well, my Sprint "Free" line is working fine. "Free" and it's working, now that's lucky! 
Explanation of T-Mobile outage. Sprint customers were apparently unaffected.