Last summer I flew into Jackson Hole Wyoming and drove to Phoenix. During the drive from Provo to Las Vegas, we stopped off at Bryce Canyon NP and Zion NP, then on to Vegas.
Don't miss Valley of Fire State Park, north of Hoover Dam. The NP pass was the best investment we made all year. I'm leaving Friday to head back to Arches NP and Canyonlands NP.

There was little phone reception off of 15, which I imagine you'll be on. With the Olympics construction and the anticipation of the SLC to Vegas runs, if you stick to the highway, you'll be fine. In the parks and winding aroundthe mountains there is little to no reception.

Enjoy!!