I have a desktop application from particular telephony provider and I want to have click-to-call functionality in GHL CRM. Desktop application can initiate the call if the phone number in web page has 'tel:' protocol prefix.

Can I using the custom JS in private marketplace app add the button in contact page in contact details which will read contact phone number and add the 'tel:' prefix, so clicking on that button I will initiate the call using my desktop app?

Or can I achieve the click-to-call functionality in some other way?