Are the Internet connections and VOIP on cruise ships reliable ?

I have a small business that I need to send and receive phone calls a couple hours a day . Can I use a VOIP connection like Skype or Vonage ? Or is a cell phone a better option ? What expenses are involved ?

Our cruise sails for 7 days from Puerto Rico to the Southern Caribbean Islands . I would need to make and receive around 5 calls a day for 3-4 of the days .

Thank you for your help .

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