Right, mate. First thing to know: WhatsApp IS Mexico. Forget regular calls and texts. Every business, every landlord, every mate you make here communicates through WhatsApp. So yeah, you need a local number.

Telcel is the biggest network. Pop into any OXXO or Telcel shop, grab a prepaid "Amigo" SIM for about $200 MXN, and you're sorted. The plan you want is "Paquete Amigo Sin Límite," $249 MXN/month gets you unlimited calls, 6 GB data, and unlimited WhatsApp and Facebook. That's about $14 USD. Proper bargain.

If you want postpaid (better value, requires an RFC or Mexican ID), Telcel does $399/mo for 10 GB plus unlimited calls including to the US and Canada.

AT&T Mexico is worth considering if you've already got AT&T in the States. Roaming works great. Their prepaid is $299/mo for 8 GB plus unlimited social media. Coverage is slightly worse out in the sticks but perfectly fine in Playa.

Movistar is the budget option at $179/mo for 4.5 GB. Does the job in the city.

What I'd do: grab a Telcel prepaid SIM from the shop on 5th Ave ($150 MXN for the SIM itself), load the $249 package, and get on with your life. Upgrade to postpaid later if you stick around.

Oh, and before you cancel your home number, port it to Google Voice for $20 one-time. You'll still get US calls and texts over wifi. Cheers.