FWIW,
Almost every year for the last 20+ years I've been to yosemite.
Verizon has a tower somewhere in or pointing into the park and has coverage in the campgrounds.
Sprint, text messages and voice work.
ATT & Tmobile sort of have coverage in certain locations in the valley.
I found all this out because my family that went all had different providers.
18 months ago, when I went the last time, I actually was working on my verizon Jetpack and did some testing - I was able to stream and such.
I don't know if the other vendors (e.g. Visible - a verizon subsidiary) or other MVNO's will workin the valley.
