The back and forth had already begun when Musk reportedly put down "moats", which Buffett has defined as a business's competitive edge, according to CNN.com.
The 87-year-old chairman and CEO of Berkshire Hathaway admits he's "too much of a technophobe" to be able to use his smartphone. "You're just hoping the next guy pays more".
Buffett said that his company owns about 5% of Apple stock right now, and wants to own more: he'd "love to own 100% of it".
"I would suggest that they need to also be open to a new, decentralized, digital, global currency. Now that is not something, I think, the world needs", he said.
Apple said that customers chose the US$999 iPhone X "more than any other iPhone each week" during the March quarter like they did in the December quarter.
The investment also helps Mr Buffett deploy Berkshire's cash and equivalents while he looks for his first major acquisition since paying $32.1bn (Dh117 billion) for aircraft parts maker Precision Castparts in January 2016.
He therefore predicted that "Cryptocurrencies will come to a bad ending because nothing is being produced in the way of value from an asset".
Billionaire Bill Gates is a notorious bitcoin skeptic who says he would bet against it if he could because he believes cryptocurrencies are worthless investments that people profit from by pawning their holdings off to a "greater fool" than themselves.
Both Democrats and Republicans in the USA believe in the benefits of free trade, he said. It's wonderful because it does create a rising price, it does create more buyers and it's better if they don't understand it.
One fund manager asked why Buffett was not investing in China. 'But both that and my stupidity have cost us a lot of money'.