By Brendan Sasso - 04/19/12 07:40 PM EDT
The FCC had drafted rules to require the notification system but put the regulations on hold after the companies' commitment.
At the time of the announcement, FCC Chairman Julius Genachowski said he would take a "trust but verify approach" to ensure the companies complied with the guidelines.
Under the plan the companies agreed to, they will have to offer alerts by October in two of four areas: data, voice, text and international roaming. The carriers must provide all four alerts by April 2013.