Some AT&T customers in several cities across the country have been experiencing difficulty placing 911 calls.
Calling 911 for a non-emergency situation ties up important lifelines meant for people or property in immediate jeopardy or when there is a crime in progress.
AT&T issued an apology "to those who were affected".
It's not clear what cause the outage or when it will be repaired.
Chester County's Director of Emergency Services Bobby Kagel says their counterparts in Delaware County spread the word that AT&T customers weren't getting through to 911. AT&T competitors, such as Verizon and T-Mobile, may seek to use last night's outage to argue that they offer more reliable service....
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AT&T has 147 million wireless customers in the US and Mexico, according to its website.
AT&T hasn't confirmed the cause of the outage other than saying it was a "service issue".
Keller, Colleyville, Wylie and Highland Park have taken to social media to report the outages.
Have you been affected by the AT&T 911 outage?
"The FCC's public safety professionals are on the case", Lisa Fowlkes, acting chief of the FCC's public safety and homeland-security bureau, said in a prepared statement.