I accidently found out my cell phone worked in Puerto Vallarta. I use Tracfone, because it only costs me $8.00 a month. It cost me nothing to call and receive calls in PV. No long distance, no roaming, no international rates. I buy minutes for about $.10 each (included in $8.00).
Since, today, you can buy a phone from Wal-Mart for $12.88, which includes a "double minutes for life"
plan, you buy the phone, purchase a card for half the minutes you expect to need, and have a phone for the time in Mexico, and you can keep it as an emergency phone for $5.00 a month (or $10 with 50 minutes added each month) The minutes never expire if you keep the phone active.
There is no cheaper way to have a phone. If this special is gone, they always have something similar.