T-Mobile, Verizon and at & T customers were mystified on Monday when their calls stopped going through. Around 1am Tuesday, the company tweeted that voice calls and text messaging services had been fully restored.

T-Mobile confirmed that it’s working to fix a voice and data issue that has been affecting customers around the country. Reports spiking around 2:20 PM et Monday.

Verizon said it was not to blame for a multi-network outage. People reporting failed calls do n’t always know which carrier their recipient is using.

As of 6pm ET, T-Mobile had already restored data services. But was still struggling to return phone calls to normal.

Teams work as quickly as possible to fix the voice & messaging problems some are seeing. Data services are now available and some calls are completing.

As of nearly midnight et, six hours after that update, T-Mobile was n’t quite finished yet yet yet. T-Mobile CEO:’it may still take several more hours before customer calling and texting is fully recovered’.

Multiple verge staffers were unable to place calls on T-Mobile on Monday. Sprint, now a T-Mobile subsidiary, and US cellular were also experiencing problems.

T-Mobile said early Tuesday morning that it was an’issue’ that has created significant capacity issues in the network core throughout the day. Earlier this evening, the FCC chairman tweeted that the outage was’unacceptable’ and that the FCC will launch an investigation.

Security researcher Brian Krebs, who knows a thing or two about DDoS attacks, tweeted that there’s no indication that the outage was related.

There may be Sprint/T-Mobile issues related to a wonky update in the systems from the Sprint side to help merge with T-Mobile. I have found no indication these outages are DDoS related.

T-Mobile’s blog post, the DDoS rumor, and the FCC chairman’s Tweet also included Tweet.