Authorities initially believed that T-Mobile phones were somehow inundating 911 with ghost calls, which are automatically generated by a phone, unbeknownst to its owner.

But officials said Thursday that it was actually abandoned 911 calls that were a source of the problem.

Callers would hang up after dialing 911 and dispatchers were then obligated to return the call to determine if there was an emergency. But that created a long backlog of calls.