I'm just hoping that the features we currently use in Skype will be ported over and made available on Teams as well. Free video calls will obviously be there, but I'm curious whether international calling (paid-for of course) will also continue...

You can run down the credit you currently have with Skype or Teams. They won't allow you to load your Skype account with any more credit. Also no more Skype In calls.

So if you use it calling or receiving calls from real phones then you need to look for something else, otherwise you could carry on with Teams (if you like Teams) if only to use up your credit.

Skype is retiring in May 2025: What you need to know

The good thing is that they're not pulling the plug completely but will allow you to use up your credit even after the Skype shutdown, as apparently the "Skype Dial Pad" will continue to be available.

Had I known I would have topped-up my account earlier, but I've still got enough credit for my "light" calling needs for at least a few more years...

If you need to call phones as well I guess the closest thing to Skype is Viber. Can't receive calls on a number with Viber though.

I used to use Viber to call UK phone numbers using the Viber out on their app. I worked fine but found Moremins which was cheaper per call and had the ability if I didn't have WiFi or data to use the free national mins on my Spanish SIM to call a UK number . As you say Viber is another useful option to call UK numbers.