There still a couple of problems that still haven't been addressed (or just aren't included in this article)
1. 1 Cell site isn't enough to cover a densely populated area. Although this is running on 850mhz which is much lower than wifi at 2.4ghz, multiple cell sites are usually better than 1 big one. If their peak is only 189mbps, then it should be fine using cat6 cable, however your limited when for range as you will run in trouble if you run cable over 100m without a repeater or booster. The other option is to use fibre, which is rather expensive but it wouldn't be that bad for AT&T considering their size.
2. Limited to the network beyond the cell towers.
This is coming from experience being at large festivals like Coachella, but although you can get signal on your phone most of the time, sms is virtually useless since your txt's are delayed by 4-5 hours. You can make a call after about trying 10 times, but because of the noise, you can never hear what the other person is saying and vice versa. So unless they are running a local relay for text's and transferring calls, their network servers are the ones that need beefing up rather than the towers themselves.
Now I'm guessing people are going to be using data more than anything, but in the past I've found 2g to be much more reliable (3g flatout did not work at the last festival, Big Day Out I was at). We found that Whatsapp became the most reliable way to communicate between our friends as your messages wouldn't get delayed for hours.