The calls I am making will be from the UK on a PC or smartphone to Costa Rican mobiles.
I put call.com on my phone but didn't like the pricing structure so got rid of it.
Next, I tried MyTello which had reasonable prices (about 1p/minute more than Skype), no subscription required, and which connected quickly to a perfectly clear line with no delays during the conversation. That'll do me!
The prices shown on the websites of all of these apps seem to be different from the actual prices, perhaps due to local telecoms charges. Many of them require a monthly subscription of around GBP5 plus the call charge, so overall costs/minute will depend on how you use the service.
References to WhatsApp above are pretty much irrelevant to this thread because they don't connect to landlines or mobiles as per the OP's query.
I didn't seriously consider Teams for three reasons:
- It's Microsoft!
- I was told it is expensive for foreign calls to landlines and mobiles (I didn't check for myself)
- Way over the top for making voice calls