Please note: Area code 315 is actually a NY area code located around Syracuse.
Before the elections, I received several political calls from this area asking for support for GOP.
The other area codes are indeed offshore numbers.
I have included the territories associated with the area codes given by Flyboy and a few extra that I could find on the Internet.
Not all of the areas below will charge the premium collection fee and per minute charge, but may end up costing extra for calling outside of your available free areas.
242 - Bahamas
246 - Barbados
264 - Anguilla
268 - Antigua and Barbuda
284 - British Virgin Islands
340 - US Virgin Islands
345 - Cayman Islands
441 - Bermuda
456 - Used for Inbound International calls
473 - Grenada
590 - St. Barthelemy, St. Martin
649 - Turks & Caicos Islands
664 - Montserrat
670 - Northern Marianna Islands
671 - Guam
684 - American Samoa
721 - Sint Maarten
758 - St. Lucia
767 - Dominica
784 - St. Vincent & Grenadines
787 - Puerto Rico
809 - Dominican Republic
829 - Dominican Republic
849 - Dominican Republic: Santo Domingo
868 - Trinidad and Tobago
869 - St. Kitts & Nevis
876 - Jamaica
939 - Puerto Rico