My Tmobile form US let me call free US and Canadian numbers while on wife outside of US. Few times I've got calls from US when I was 'outside' of wifi and Tmobile charged me 10c per minute for that call (I think that was for incoming calls). For outgoing calls without wifi they charge 25c be it US number or European/Asian number.
I spent hours on the phone when working in KSA (with the customer in US). Because I was on wifi the calls were free.

Speaking of Tmobile. How to add ESIM to iPhone 14 or 15 when you want your primary number to stay and have ESIM from another country as a secondary number and internet provider when you are in that country?