The city of Dallas confirmed Monday that 442 callers to the city's 911 system on Saturday were placed on hold. It's the latest emergency services bottleneck that mobile carrier T-Mobile is responsible for, according to the city.

Sources told News 8 the average wait time for callers was 38 minutes on Saturday.

This comes after a memo from a Dallas assistant city manager saying T-Mobile "still does not know what's causing the problem or how to fix it," according to Eric Campbell.

WFAA first reported the problem with "ghost-calling" from T-Mobile phones in early February.

When T-Mobile customers call 911 their cell phone repeatedly dials 911 causing police get multiple calls from the same number.

The hang-up calls require a call back which creates a backlog for callers, no matter their carrier.

T-Mobile did not respond to a request for comment Monday on the memo from the city of Dallas or progress on a solution.