T-Mobile with iPhone 6, 6s, and 8 = nothing (as of June 17 - are they supposed be upgrading? Sprint hardware?). The only place I get (weak) reception in the park is at the hairpin next to Dege Peak. On the south side, I have to drive to Eatonville. Seems like Verizon people have no problem at Paradise . . .
Today, July 10th, I got three bars at the Paradise Visitor's Center and great reception @ 8,500 ft. It's a new iPhone SE, FWIW. Bonus is 1 bar reception between Easton and Ashford, which has always been a dead spot.
