Yeah... there's no excuse for any carrier to take that long to activate a SIM. If ATT is strong in your area, tell your current carrier 🖕and go to Cricket. They're on ATT towers, and other than being drastically cheaper, the service is exactly the same. No contracts, and no surprise bills, ever. (Ie: $30 plan is $30, period... taxes/fees included).
I've been with them for about 6 years now, and don't have a single bad thing to say about them (sans their over seas support after hours). One thing is for sure, they can fit and activate a SIM in <5 mins in store, and they're everywhere now. (Hopefully somewhere near you).
I dont think it took 72 hours to get my first 'bring your own' phone going through Cricket, and that was even after ordering the SIM kit online. The setup kit arrived on day 2, and it took less than 10 mins to have my phone setup and fully functional on their system. ✌