AT&T is notorious for no coverage on Whitney. I never had a single bar on my phone either trip up the mountain.
ATT is complete garbage around Lone Pine - my phone only works OUTSIDE of town heading north on 395, while my son's works just fine in town, both ATT, almost identical models. We once got a call near Lone Pine Lake coming down from Whitney, but never were able to replicate that from up there with the same phone.
Meanwhile, back on the other side of the Sierras at Lake T Edison, ATT is what you need - you can call even from the far end of the lake where the ferry picks you up while Verizon users have no signal.
Verizon is what the locals around Whitney prefer, but it's still a hit and miss on the mountain - most phones are too weak to initiate a call from the summit. The Portal store has switched to a satellite phone to have reliable communication.
