So I started a plan on Fi... was working fine on T-Mo HSPA+, I saw the prompt to improve service. Now, it's connected to weaker Sprint LTE and I am unable to call out. 
Calling the phone, it rings on Hangouts but not the phone.
On Fi Chat waiting for assistance...
Have you already tried toggling airplane mode and/or power cycling device?
Your not alone. Maybe these links will help.
No, because it said I will be out of service for a few minutes then get service back... did not want to mess it up if it's still configuring... waiting on support... queue is long but goes fast.
OK, waited long enough... tried airplane mode, did not help. tried reboot, did not help. When calling, it actually says to call customer service, so I am still on the queue...
Well, after restarting, it tried to acquire Sprint DM again (I guess it had gotten stuck), now I get a diff msg when dialing out (we are unable to complete your call at this time)... I am able to dial in and answer the call.
still on the queue...