I do most of my riding around Tucson, not too far from you I guess, and I've felt a lot better about having a SPOT with me as I typically ride solo myself.
Some of the higher end SPOT units have 2-way messenger capabilities, but they will cost you as I'm sure you know. I for one have been truly surprised at the voice and even data reception I've been able to get on my phone many miles from a paved road, so long as I'm on a ridge!
I carry the more basic SPOT Satellite GPS messenger with a couple of add-ons. You know those cool SPOT track maps?
$50 a year extra actually, but it's one of the coolest things about having a SPOT so I think it's worth it. It's nice to be able to go poke around and later look up exactly where you were.
And for an additional $13 a year, the GEOS search and rescue insurance seemed like a good deal to me. I see the $100K airfare medevac choppers landing on the hospital by my work every day.
Even without the additional services, you can call for help and send previously entered messages via email and text while you're way out. I recently opted to hike out of a riding hiccup for several hours without water instead of using the SPOT, but if I'd been farther afield or badly injured it could have saved my butt.
Not a bad last-ditch option to give yourself if you ask me. I'm a satisfied customer.
That's my $0.02