1. How do I activate my SIM Card?
Telcel SIMs come already active, you only need to insert it in your phone while arriving in Mexico. It can also be tested in the US before leaving. Movistar SIMs will activate upon inserting them in the phone and you will receive a text message with your phone number, which will be a local number from the region where you are activating the SIM. Iusacell SIMs needs to dial a number and hit 2 numbers to get activated.
2. What does it mean for a phone to be unlocked?
It means that your phone is able to work on more than one network. Generally, an unlocked phone has been purchased at full price from the retailer (Directly from the Apple Store for example). Alternatively, a phone can have been unlocked by your service provider at your request (some providers can grant a temporary unlock) or with the use of unlocking software by a third-party.
3. What SIM does my phone use?
You will be asked at checkout for the required SIM size for your phone. You can see what size your phone uses here or alternatively you can indicate your phone model at checkout.