Skype
Well, Skype is bollocks anyway. If you want to sell telecommunications services, you have to communicate nicely with other people. Using your own jealously-guarded, proprietary protocol while others around you are using an open, published protocol would be a recipe for alienation even if you were first to the table.
The minute Skype is made compatible with proper VoIP (for which read: Asterisk), there's suddenly no reason to be using Skype as opposed to any of the existing applications which use the open IAX protocol.
Come to think of it, anyone with an IAX-compliant application that is easy for chavs to download could knock Skype off their perch.