Looks like Sprint continues to have some growing pains. Apparently they had a slight outage in New York City today and attribute that outage to a downed VoIP switch:

Quote Originally Posted by Sprint
One of our VoIP switches in New York did experience an equipment failure earlier today causing some traffic to be rerouted to another switching location during the repair process and resulting in call congestion for some Sprint customers. Our network operators are working aggressively to resolve this issue and hope to have service back to normal soon.

Source: Sprint voice service down in New York City (updated with official statement) -- Engadget