AT&T’s issues are not primarily around spectrum or backhaul. Instead, they center around 'signaling', which smartphones rely on for polling, status and control updates.
But here’s the fascinating point: the signaling issues aren’t just AT&T’s fault. In a quest to extend battery life on the iPhone, Apple did something 'non-standard' which compounds the issues – the iPhone constantly drops connections, going in to an idle state. Keepalives within the apps then reestablish a new connection after only a few seconds. Network equipment makers never anticipated this. Think of it as hanging up during a phone call when the line is silent, and then redialing to respond.
[btw: http keep-alives were created as a solution to this kind of network overload.
With http, the keep-alive means, don't close the connection too soon - - keep it to allow another transaction ]