Earlier quoted context omitted.
Because you may not be calling from a cellphone, but from a land-line. Nothing about the number displayed on the app means that you have to use the device in your hand to dial it. edit: actually, it does look like the desktop landing page explicitly suggests that this is what it's for.
I would still just call any random ANAC and have my number read back to me on the call instead of using this service to setup a session online, call the provided number, and then return to the web session to learn my number. There are plenty of well known ANACs, like 1-800-444-4444
> There are plenty of well known ANACs, like 1-800-444-4444
Hey, today I learned something new!