EE just became the first UK carrier to support Smart Number technology. It allows you to use your iPhone’s number to make calls or send texts with an iPad or an Apple Watch or even a Mac or an iPod.
You need a “main” device – iPhone 6 or newer, it has to be an iPhone and it has to run iOS 11.3 or later. Then you can pair up to 5 other Apple devices such as an iPad, Apple Watch or even a MacBook - you will find the compatibility list below. Best of all, the service is free.
Once paired, incoming calls to your main number can be received on any of your paired devices. And outgoing calls from any device will appear to be from that same number. You can even start a call on one device then hop onto another device.
The paired devices don’t even need an EE SIM card, they just need to be connected to the Internet – over Wi-Fi or another carrier’s data plan (half an hour of talking uses up around 10 MB of data). Do note that when you are abroad, Wi-Fi calling from the paired devices would not work. But if these smart devices are still in the UK, they will also ring even while you are outside the country.
If you are wondering why the service is only available for Apple devices, the answer is it's using a feature, which is built into iOS itself. It's called 'Wi-Fi Calling on supported iCloud-connected devices' and so far it was only available Stateside and in Hong-Kong although it's available under different brand names.