Most folks don't buy another phone and the carrier makes a bundle on $2/min calls from the foreign country.
The smarter folks buy a cheap $30 GSM/CDMA phone before the trip, the even smarter ones have a world phone and confirm it's capable of taking foreign sims (though having a fallback $30 GSM phone isn't a bad idea).
> having a fallback $30 GSM phone isn't a bad idea
Especially if you need to use SMS two-factor authentication on your normal home number. Trying to make a bank transfer when the code is sent to SIM A and the data plan is on SIM B is otherwise an interesting challenge. (That's the voice of experience.)
The smarter folks buy a cheap $30 GSM/CDMA phone before the trip, the even smarter ones have a world phone and confirm it's capable of taking foreign sims (though having a fallback $30 GSM phone isn't a bad idea).