There's 3 types of international calls that save money compared to actually making an international telephone call.
1. Friends, family, anyone who is reachable over the internet: use whatsapp, messenger, or any app in Crystalhead's list above, common requirement is that both parties have the app.
2. Calls to companies / parties who only have a phone number but don't need to call you back: use voip calls (Voice over ip) through something like DialNow to make a cheap call (for most countries around 2 cents per minute or less) where at your end the call is made through an app (internet) but in the receiving country it gets directed to a regular phone number (landline or mobile).
3. When you need to be reachable without the other party incurring high costs to call you, and you wish to enable that: you need a local number in the country of origin with a forwarding service for calls through the internet.
I would say though that if it's really urgent they can place a short call directly to my number here after which I can call them back. If a 2 $/€/£ call is too much to ask in an emergency then pffft.

 

https://callhippo.com/signup/united-kingdom-phone-number/