It all started out great today. I convinced my family to go onto a T-Mobile One plan, and on top of it was able to reserve a T-Mobile 7 Plus for pickup at the local Apple Store. I opened a T-mo account and took the active SIM to the Apple Store where they gave me my 7 Plus. Then, one by one, the family members pulled out of the arrangement, for various reasons, leaving me with my current AT&T account and a new one from T-Mobile. The iPhone was still wrapped so for the heck of it, I opened it and put my AT&T sim card in and powered it on. It immediately grabbed an ATT LTE signal and I was able to make calls without issue, even after signing in to iCloud. So my question is, does anyone know if I can just cancel the T-Mo contract and keep using the phone with AT&T, while making payments on the IUP for the next year? Thanks for your help here!