Will my CheapESIM work on ferries to Martinique or Guadeloupe from Dominica?

No, this specific CheapESIM plan is strictly for use within Dominica. For island-hoppers, it's crucial to understand that Martinique and Guadeloupe are French overseas departments and thus part of the EU, while Dominica is an independent nation. Your CheapESIM data connection will cease once your ferry exits Dominican waters and enters French/EU territory. To avoid unexpected roaming charges or loss of connectivity, CheapESIM recommends purchasing a separate, cost-effective plan for these other islands if your itinerary includes them.