Going to Cabo San Lucas. Will my cell work there?
Mexico is included as part of international coverage; however, there's no telling about data service as foreign carriers don't necessarily have the same technology as US carriers. If you're somewhere where they're still on 3G or earlier wireless technology, your apps aren't going to work.
If you are postpaid, you'd enable roaming on your phone and will get notification that TravelPass has enabled for a 24 hour session. If you're using Unlimited Ultimate, TravelPass service is already included in your service plan so you don't pay the extra charges for TravelPass.
If you're prepaid, make sure the TravelPass toggle is enabled in your account before leaving, and load funds into your account to cover the daily costs of TravelPass. Otherwise, a prepaid line doesn't work at all outside of the US.