Originally Posted by RobUAIntl

The O2 Travel Esim allows local calls within country for every country in Europe. That is if you're in Italy, you can call Italian numbers for free. But if you're in a different European country and want to call Italy it doesn't work. Sometimes you need to call using the full country code plus phone number (+39 for Italy) and sometimes just the local phone number starting with a 0 (zero). It seems to vary by country and sometimes by phone number within country so some trial and error might be needed, but it does work and has no added charges. I use it for restaurant reservations all the time.

You can also call a UK number from anywhere in Europe for free as long as that UK number is in the UK (and not roaming in Europe)