I hiked the Grand Canyon last weekend. I did not take my cell in with me but others did. I made a call and text from the 1.5 mile resthouse on Bright Angel using a friends phone.

Texts work on less 'bandwidth' than calls but you still need an active signal. IME, I have tried many times sending text just outside a signal area under the impression it would continue to resend until I walked into the signal in the next ten minutes or so. This is not the case with my phone. It alerts it cannot send it and goes to drafts.