Nobody seems to have mentioned this yet: Wi-Fi is good, but you need to sit by the bathrooms.

No T-Mobile but fast free WiFi

We both have Verizon and we could not get any reception at the campground down by the river. We had to hike or drive out of the canyon up to the main part of town to get a good signal, so you may need to drive and campout for the day up in town.

Great campground, but absolutely no signal from Verizon. We had to hike out to the beach to get any reception. No experience with AT