Call your provider or visit their website. It all depends on your plan and provider.
I have Verizon and "regular" users will see a $1.99/minute for voice usage in USVI and .99/minute for Puerto Rico.
I have an International Roaming plan and these calls are included. If my wife uses her phone then the rates apply. It isn't worth switching over unless you plan on doing a lot of International travel.
All plans and providers are not equal.