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No. WhatApp uses your phone internet data connection or WiFi where available, calling also works the same as sending messages.
Please see here: Is it free to send messages over WhatsApp?
If you use Google you will also be in a position to see further information for using WhatsApp.
To call the Rupublic of Ireland using your phone, you will need additional credit, I would recommend adding Vodafone International, still free for PAYG. Details here: Calling and Texting Abroad
There's no additional charge to use your data, minutes or texts in any of the 48 destinations in our Pay as you go Europe Zone [PDF: 677KB]. If you have a Big Value Bundle you can use your inclusive data, minutes and texts at no additional charge. Extras and Freebies can also be used in our Europe Zone. If you don't have a Big Value Bundle, Freebie or Extra you'll simply pay the same for data, calls and texts as you do in the UK.
You can use whatsapp via wifi too.
Current Phone > Samsung Note 10+ 5G _256Gb > Model: SM-N976B.
Samsung One Ui 2.1 / Android 10.
Samsung Gear s3 Frontier Watch.
Samsung Galaxy Buds.
Many thanks for info on Whats App video calls to Republic of Ireland on a Pay As You Go deal. For a newcomer the information often varies and your response is reassuring.