Even if nothing worked, it should still open a box asking what application to use..
You are only going to be able to do this using a device with phone options.. Not sure if you can do it using a Mac or PC with some kind of software to act like a telephone..
You might have to wait until Monday for Gerald the guru on all this coding stuff... I just blindly fiddly until stuff works..
There is a new Plugin 'PanoTag' but that just a social media thing.. It would have been handy for that to have this feature.. Perhaps ask for it as a Feature Request.. emmm Just another one to fall into the dark void of lost suggestions... Never to see the light of day...
Well, using a hotpot you can add that into any Pano within the Tour.. But to use a Button you will have to make that Pano specific so you will need to copy the button code, and past it within the pano located in the main xml file.. Then remove it from the Tour in the Skin..
All you need to do is create a small web page as fancy or basic as you want.. Then in PTP add a Website Box.. Then add the Button or Hotspot linking it to the Website Box and then provide the url... phone-button.html etc.. In that page you just need to add the <a href="tel:PHONE NUMBER"></a> There might be a neat way of doing it.. When the user clicks on the link, it will automatically option their phone to dial.. I cannot work out how to auto dial.. Again their might be a way to do that..
What I did was just a mockup to test its function.. you could make the Website Box with no boarders, perhaps that might look good..
There might be a CallMe widget that could be added to a Tour...