Verizon service (in my case) is very inconsistent and generally unreliable unless you are up high on the rim or on a plateau (Full bars and full data). Strange as it is I was able to make calls from the bathroom area at the South Prong Primitive camping sites.
There is T-Mobile service at the Little Red Tent Camping Area if you're right next to the bathrooms, otherwise there is not. I haven't camped in any other area but generally service with T-Mobile comes and goes around the rest of the park, even between individual camp sites.
It's spotty and it depends on the camp site but for the most part, Yes.
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