Since Skype credit stopped working, I put $10 on 'Viber Out' for similar treatment, i.e. making calls when you have a data only esim or wifi, to local numbers/landlines.
Used recently in both ZA and NZ for about 8 calls all up and worked well. Spent about $1 total, rates to ZA a lot higher than back to AU and NZ, you can check their rates online and is generally per minute. You can also buy specific country packs but they didnt interest me
Skype credit saved my bacon a couple of times in the past, for example: a ticketing issue flying KLM on a VS reward ticket when the check in person says not their problem, call VS to resolve. Very handy to have a means of calling a real number!