If you have AT&T you can use the method that you described. However, the people back home will not be able to call you and have it be a local call (I think). With talkatone you don't need any particular carrier and the people can call you anywhere you are from the states and it's a local call for them since you'll have a U.S. number.
I used WIFI calling in SXM with AT&T and since it was my home number, there was no problem and no charge for people at home to call me in SXM.
It was a local call.
When I called a restaurant in SXM, that was international, and cost me under $2.
No charges with Whatsapp on WIFI either. Didn't use it for any calls in SXM, but I've heard that many places have it.
Then that would be free.
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