Calling UK?

I suppose the other strategy could be to have frequently renewing SIMs for UK networks and toss or retain for later use when calling home from abroad no longer works. Moneysavingexpert recently listed some networks still with a level of roaming coverage, you could investigate some very very low contract prices or payg there.

Absolutely - WhatsApp is great.

You don’t even have to ask someone if they are on it. If you have a person’s mobile number in your contacts they will come up as a WhatsApp contact if they are subscribed.

WhatsApp can also be used for it’s primary purpose, as a text messaging app, but is very good for voice & video calls too.

You can also use Facebook messenger in the same way as WhatsApp.

These days I find things like Skype a bit clunky & unnecessary.

Agreed. As much as I hate Facebook / Meta, they’ve done a better job with WhatsApp than Microsoft has with Skype.

If WhatsApp worked on my mother’s Amazon tablet then we’d use that, but it’s not compatible so I have to make do with Skype.

It would be better if it worked on more than one device though.

If you mean WhatsApp I use it on my iPhone, my laptop & my desktop.

You cannot have it on two devices if it’s the same operating system on a phone, phone & laptop/desktop yes, two android phones or tablet on older devices or versions of WhatsApp, it’s just started on newer versions up to 5 devices since May.
Companion mode I think they call it now.