Sorry, I'm not at all an IT guy ... but EVERYONE in Baja (and Mexico in general) has a Cell phone. My phone did not work beyond the border ... but some can be set up to work world wide. (see IT guys for this info)
Friends who LIVE in Baja buy a local SIM card at the border and plug it into their phone. The local Phone Kiosk kids (everywhere!) are wizards at doing this and can set up your phone in seconds. SIM card is pretty cheap, IIRC.
All over Baja you see (sadly) "Microondas" towers. Man, those microwave towers are frikkin' everywhere! I see everyone on the phone ... so I'm guessing coverage is pretty good. Even if you have to Buy a phone for Mexico ... it's not expensive. TRACFONE (pay as you go, includes phone) is popular down there and coverage is not bad. About $25, comes with 60 minutes, you buy more as needed. (for sale everywhere)