Using What’s App from the UK to Canada

I am not entirely sure what you are asking but WhatsApp is a commonly used communication app.....particularly for non Apple users. I video chat from Ottawa to Toronto with it. Reception can vary, but it might not be the apps' fault. It is my primary text message app when overseas as it is free and runs on wifi....no data required. I have used it in Spain, Portugal, England, USA, Mexico...... Well, you get the picture.

I use WhatsApp exclusively to speak to relatives in the UK as none of them have an I-phone. It works in both directions. (UK - USA). You will have to take your phone out of airplane mode to use it but as long as you are on WI-Fi you will not get data charges. A couple of other phone tips, You can just turn cellar data and roaming off. Reset your statistics so you know if you have accidentally used any data. Turn the majority of your apps off. Whatapp is sometimes good and other times the calls drop off continuously. Facetime works well, even slightly better.

Could your family get along with texting via Whatsapp instead of voice calls ? Works for us, but that's texts to our Millennial kids, not older parents.

Before I answered, I googled whether you could use Whatsapp in airplane mode and Yes, you can. The instruction was to turn on airplane mode and then turn on wifi and choose your server. I have been using wifi this way the past week when traveling....though I didn't use Whatsapp.
Try it from home so daughter can alternatively give you directions to disable data roaming.

As has been mentioned, you can turn on Airplane Mode on your iPhone, but keep wifi (and bluetooth) on while doing so.

Usually, the first time you activate Airplane Mode, your phone will disable cellular, wifi, and bluetooth. It will keep doing that by default, unless and until you choose to turn wifi and/or bluetooth on individually while in Airplane Mode. The iPhone then will learn that preference, and keep wifi and/or bluetooth on even when you activate Airplane Mode because it thinks that's what you prefer. This is handy for situations like yours, where you still want to make wifi enabled calls through third party apps (or use bluetooth headphones, or even connect to wifi on an airplane, or any other scenario where someone will want to disable the cellular functions, but keep other data transfer services active). Airplane Mode will always disable the cellular service, though, as that's really the defining characteristic of Airplane Mode.

Even if you activate airplane mode, then manually enable wifi, I'd still suggest going in to your Settings > Cellular > then turn off Cellular Data and turn off Data Roaming.

With the above settings, and no data plan, the iPhone might as well just be no more than a wifi access device - like an iPad without a data plan, or a Kindle or laptop computer. You can then use WhatsApp on wifi only. The signal on WhatsApp will be no different from a Facetime signal - the wifi signal coming in to the phone will be the same for all apps and functions as signal strength applies to the whole device, and not individual apps on it.

For extra peace of mind, you can set up your phone to test out WhatsApp (and your Airplane Mode, and cellular settings) at home in Canada before traveling. Once you have cellular turned off and are using it with wifi only, it will perform the same way in your living room in Canada as it would in a B&B in Wales - there's no practical difference at all. That way, you can get familiar with the settings, fiddle around with WhatsApp and test a couple calls/texts, and be sure you're all set and ready to go! Even when your daughter installs the app and sets it up for you, you guys can test everything out and be sure it's working how you want before your trip.

Have fun on your trip!! :)

Via WiFi sitting here LA I often video chat or text to colleagues in the U.K. No data usage. No cost.

And vice versa when I’m in London and want to chat with folks in the U.S.

Verizon and iPhone 7.

As I’ve noted before, learned about WhatsApp from the Chinese owner of the flat I stayed at in London in 2016.

That’s how we kept in touch once I downloaded the free APP. She was in China throughout my London stay.

For users of Whatsapp, it is worth updating your app. There's been a hacking attempt and Whatsapp has pushed out an update. I've just updated all my copies.

Not strictly relevant to the OP's question, and AFAIK does not apply in UK and Canada, but there are parts of the world where data, used for apps such as Whatsapp is charged for at different rates than "normal" data. I believe South Africa is one such country.

I wanted to add one more suggestion, just to be extra safe about not incurring any unexpected cellular data usage charges.

On top of what I mentioned in a post above (turning off data roaming and turning off cellular data), I'd also suggest turning off WiFi Assist. WiFi assist is a feature on your iPhone that would shift your data usage away from wifi and to a cellular network when the wifi signal is weak. You don't want to risk having this happen when overseas without an international calling plan, and are better off just having the call drop.

Go to your Settings > Cellular > then scroll down to the verrrrrryyyy bottom of that screen (depending on how many apps you have installed, this might take awhile as your phone loads up a display of every single installed app that uses cellular data, and displays stats on how much data those apps have used over the last couple billing cycles. It might not take too long for you if you already don't have a data plan or many apps, but other people who use more apps might have to wait 15 to 30 seconds).

Toggle the WiFi Assist option to Off (where the WiFi Assist is listed, it'll also tell you how much data you've used with this feature. Can be an interesting bit of info to show you how often your phone - on its own and in the background - switches your phone call away from wifi to your carrier's cellular network).

While one might hope this isn't necessary without any cellular data plan and all cellular functions turned off, better safe than sorry!