Best no contract service for eventual migration to T-Mo
Family of 4, currently have 2 Tello, and two Red Pocket plans. Last December, I came across a T-Mo plan where they gave 4 free 17 Pros for a plan cost of $100/m with a 24-month commitment. If I recall, they did require a port-in (I'm trying to find the details on that deal but can't), but was limited to certain carriers.
Our current phones are over 4 years old, and I'd like to take advantage of such an offer should one pop up later this year. The question is, which is the best no-contract carrier to take advantage of such a deal? Two of us (one Tello and one RP) don't care about our current numbers (so can quickly create a new line and port those numbers to T-Mo). The other two would have to port their current numbers to the new MVNO, and then on to T-Mo..