If you sign up for the ATT international plan you pay $10/day for any day you use it internationally. If you don't use it you don't pay. We had excellent signal a few weeks ago. I can't speak to Verizon at the present time but according to Baard it worked fine as well. Both ATT and Verizon allow you to make a hotspot. Both carriers are going to use the native infrastructure meaning LIME or Digicell. Which I believe means you will have the same bandwidth as you would get with the Sunsail $40/day plan. So I"m not sure why you would bother with the Sunsail plan - I don't believe it gives you anything other than a bigger bill.
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