Story highlights The boy died in March after his caretaker couldn't reach emergency dispatch

The carrier and Dallas officials say they've worked to ease the load of "ghost calls" to 911

(CNN) The family of an infant who died after his babysitter's repeated attempts to reach 911 failed is suing T-Mobile, saying the carrier is partly to blame for his death.

Six-month-old Brandon Alex's babysitter tried for 40 minutes in March to call 911 after the baby rolled off a daybed onto the floor.

At the time, the city of Dallas' emergency dispatch system was being clogged with so-called "ghost calls" -- duplicate calls generated from legitimate 911 calls, city officials have said. The problem went on for months, and has been blamed partly on an issue with T-Mobile's network technology. The city's call center staffing was also scrutinized after the incident.

In the lawsuit , the boy's mother, Bridget Alex, claims that her son's babysitter could not connect with 911 after trying several times on March 11, and that T-Mobile's software failed to provide the dispatch service with the call's location.

The babysitter on that day did reach Alex, who raced home and rushed Brandon to the hospital. The baby was transferred to another hospital, where he was pronounced dead. The boy's cause of death has not been determined, the Collin County Medical Examiner's office said.

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