Yesterday's nationwide T-mobile service outage may have been due to a system software error according to a statement from a T-Mobile spokesperson:

On Tuesday, some T-Mobile customers may have experienced service disruptions impacting voice and messaging services. We restored full service to all affected customers later in the day. After investigating the cause, we have determined that a backend system software error had generated abnormal congestion on the network. T-Mobile has since implemented additional measures to help prevent this from happening in the future. We again apologize to those customers who were affected and may have been inconvenienced.

Basically, everything should be back to normal, but if you're still experiencing service issues outside of the ordinary, please let us know in the comments.