The issue was resolved just after 9:30pm, AT&T said in a tweet. The issue was part of a nationwide problem with the phone company.
Earlier, AT&T acknowledged an issue affecting calls to 911 for its wireless customers.
"We are aware of a service issue affecting some calls to 911 for wireless customers and we're working to resolve it as quickly as possible. We apologize for this inconvenience," AT&T said in a statement.
Houston Police Chief Art Acevedo also acknowledged the issue on Twitter.
"If you are on ATT Network there is a problem if you try to call 911. This may be a nationwide issue. We are looking into the problem now," Acevedo tweeted.
FCC says it will investigate the "root cause" of the outage.
NON-EMERGENCY NUMBERS ACROSS THE AREA:
* Houston: 713-884-3131
* Montgomery County: 936-760-5800
* Sugar Land: 281-275-2525
* Fort Bend County: 281-341-4665
* Galveston: 409-765-3702
* Brazoria County: (979) 864-2392