Hi there, new expats and travelers!! I actually created the bulk of this post in a thread, trying to help a new traveler to the DR. Planner asked that I cut and paste to a new thread, so future forum visitors can find this information.
If you're traveling to the DR (or most other countries these days), you probably can SWITCH the SIM Card in your phone -- that's the little brain that connects your phone's CPU to the new network you're going to be using in your new locale.
I want to point out, it is possible to buy roaming global phones for which you don't have to switch out SIM cards, which are very handy for frequent global travelers.