This gets repeated a lot, and might be true (apparently the patent lawsuit forced Apple to change the implementation to be less peer-to-peer?), but lore says that Steve Jobs announcing Facetime as an open standard was a surprise to everyone working on Facetime.
Not killed. Apple decided not to charge for non-Apple users and not to provide it for free either. They were only prevented from doing P2P connections, not from opening the protocol.
Or maybe it could've even been federated... not that Apple likes to play nice with anyone else.
Which is funny given that WhatsApp started as a very popular paid service. They could've been that for iMessage and extended it to calls.
You can start facetime calls from an Apple device to anyone by sending a link that works in their browser. No it's not 100% of the functionality, but it's a lot of it.