The service. When my son went a couple of months w/o using the phone (it was for emergencies only), T-Mobile deactivated the number and reassigned it. I wasn't informed of this practice and I didn't find out until I put money on it and it failed to make calls. Getting my money back was a nightmare and some of the reps were tough to understand, so there were communication issues. I finally had to do a chargeback on my credit card. Since the phone wasn't jailbroken, I had no choice but to continue business with T-Mobile and pay a reactivation fee. I've had other issues too, but they're too convoluted to go into here.