Using Apple SIM, you can choose from different cellular carriers
and their various programs. The data plans vary by carrier. For
instance, in the United States, you can choose a domestic plan
from either Sprint or T-Mobile and also pick an alternate plan
from the other carrier as needed. When you choose AT&T on iPad Air
2 and iPad mini 3, AT&T dedicates Apple SIM to their network only.
If your Apple SIM becomes dedicated to a specific network and you
want to choose from other carrier programs, you can purchase a new
Apple SIM from an Apple Retail store.
Sprint and T-Mobile leave the SIM alone.