T Mobile Roaming Costs?

Phone plan the person uses is the tmobile 50 dollar plan that includes unlimited everything. The person i know will be going to europe and would like to call back to the usa while in europe. The person is going to Greece.
Does anyone know how much it cost to call back to our home in the usa?

I know a person that will be going to greece for a vacation. They have tmobile and have the unlimited everything plan. I believe tmobile allows free roaming to many countries and you get free data roaming though i read its 2g only and you could text as well. Phone calls to the usa are 20 cents a minute i believe from greece.
The person would like to make phone calls to the usa from there but obviously would like to talk more than a few minutes. Is there any other option besides this? I believe skype is the only other method but if you use skype you either need fast wifi or a fast data plan which i assume 2g wouldn’t be fast enough?
I saw this posted in another site

Calls to the US:
Cellular calls: $.20 per minute
Wi-Fi calls: FREE
Cellular calls obviously mean you are in greece and calling to a usa number. But how does one do wi-fi calls?

Is the other option use skype to call? Thus use the 2g data or the free wifi in greece then call from a skype number to the usa? If so its 1.7 cents a minute? Does this apply to being in greece and calling to a usa number?

T-Mobile probably knows.