I have ATT service and have had sporadic phone reception on portal road all the way to the portal parking lot. Reception at the portal was 0-1 bar depending on where I was standing. On the trail experienced several spots where I had receptions but don't remember exactly where. Some texts and email came in on my phone and as able to respond to them on couple spots but the majority of the trail there is no reception.
I did not try to get reception at the top this year because I was too busy watching the sunrise but I remember a friend and I had some reception last year at the top but it was hit and miss. Turned on airplane mode, turn it off, search for signal, had no success. Move around, tried again... etc..
Short answer. Unreliable reception at best with my experience.
