Tom the tipster writes in:

Just a quick tip: T-Mobile is offering a set of plans that allows unlimited calling to five numbers (their "my-faves" plan). However, they advertise that you need to buy a new, compatible phone to receive this service. This is simply not true. Although the service reps claim otherwise, you can actually sign up for the service and simply use the new SIM card you receive in any phone. After confronting several service reps about this, I was told that this is in fact true, but that they are "not supposed to tell anyone."

From T-Mobile's Website:

"Limited-time offer; subject to change. Available solely with myFaves-enabled handset. Each person on a myFaves for familes plan must have a myFaves-enabled handset. Two-year service agreement required."