We agree with Wikipedia that click-to-call (CTC) is actually a misleading name for this technology as it typically refers to a means for web users to ask a website operator to call them, in other words "click-to-call" would be more accurately referred to as "request-a-call".
While these "request-a-call" style applications are popular and easy to setup, their limitation is that they can only work when web users have a phone.