Telus Extend doesn't work with the Apple Watch and it does not mention Apple Watch in the App Store description either. It's different than Apple's wifi calling feature which is currently only available on Bell, according to Apple's website. Extend is an app that is more like Skype in that it does calling and texting from within it's own sandboxed environment.
Wi-fi calling as designed by Apple is very different than an App. In addition to seamless handoffs between wi-fi and cellular, there is no conflict between the App and regular calls when in a cellular area, and a number of other issues.
Telus Extend is more like a VoIP app than a truly integrated solution, so, as @Nighthawk stated, the two are not the same.
You would have to Call Telus and explain your situation. I lived in a ciity for a while that had horrible reception and dropped calls and was near a tower. I was given Telus Extend as a stop gap when i was home, so i could have semi normal service. Which worked great by the way.
Usually if you have spotty service you will be given Telus extend.
@WestCoasterBC has the best use situation. If you have a good cellular signal and Telus Extend in use, you could have an experience like I did - every device in your house is ringing on an incoming call, from two sources! I now use it on rare occasions when in a location with Wi-Fi, but poor or no cellular service.
it would be nice if it could automatically hand off to Wi-Fi when available to reduce the loading on the cell network in crowded locations.
How would one go about getting an invitation to use Telus Extend, or when this will be available to the masses? I have a remote property that is out of cell phone coverage and would like to be able to use my cell from time to time on my wifi. I know this option is readily available for all rogers customers and am starting to wonder if I should be looking at making the switch?