Sprint phone? That was probably the Sprint customer service people calling you. I've had em do the same thing when my payment didn't go through online and they said I had a past due amount. Don't have the number on my phone any more to see if it's the same.
Ahhhh.. there it is. Yea, that's the Sprint folks giving you your disconnect notice. (it was in my missed calls section, I guess I missed them calling me one time)