WASHINGTON, Nov 23 (Reuters) - T-Mobile USA (TMUS.O) agreed to settle a U.S. probe for $19.5 million after a massive 2020 outage led to more than 20,000 failed 911 emergency calls. The settlement was prompted by a Federal Communications Commission investigation into a more than 12-hour outage in June 2020 that led to congestion across No. 3 wireless carrier T-Mobile’s networks, and caused "the complete failure of more than 23,000 911 calls." T-Mobile as part of the consent decree with the FCC has also agreed to make new commitments to improve 911 outage notices. An October 2020 FCC report found the T-Mobile outage disrupted calling and texting services nationwide and access to data service in some areas. It resulted in at least 250 million total calls failing.The FCC estimated "over 250 million calls ... from other service providers’ subscribers to T-Mobile subscribers failed due to the outage" and "at least 41% of all calls that attempted to use T-Mobile’s network during the outage did not complete successfully." T-Mobile said Tuesday it has "built resiliency into our emergency systems to ensure that our 911 elements are available when they’re needed. Following this outage, we immediately took additional steps to further enhance our network to prevent this type of event from happening in the future." Then-FCC chairman Ajit Pai said the FCC staff report showed the company did not follow established network reliability best practices that could have potentially prevented or mitigated the outage. The FCC report said the outage was caused "by an equipment failure and then exacerbated by a network routing misconfiguration that occurred when T-Mobile introduced a new router into its network." T-Mobile said earlier its network experienced an 18% reduction in completed calls during the outage but in the report acknowledged network congestion "likely required many of its subscribers to make 2-3 call attempts before successfully connecting."