Apple shareholder and billionaire investor Warren Buffett says he's not interesting in replacing his flip phone with a smartphone - even though Apple CEO Tim Cook has personally tried to persuade him otherwise.

Buffett flashed a retro Samsung flip phone during his latest interview and said he is not interested in changing - despite annual Christmas reminders from Apple's CEO.

Around 510 million flip phones were shipped globally in 2016, showing Buffett is not the only one that prefers his retro device, according to the Daily Mail.

Buffett's company Berkshire Hathaway is one of the top five Apple shareholders with share worth around US$23 billion ($31.6b).

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However, in an interview with CNBC 'Squawk box' he said he's not interested in upgrading to an iPhone.

"When I actually buy it, it's all over, folks. The last person has bought it," he said.

The investor says that despite his personal reticence in upgrading, "the market is not yet saturated for iPhones."

"Tim Cook sent me a Christmas card again this year saying he's going to sell me an iPhone this year," Buffett said.

"He keeps sending me these reminders every Christmas."

In the same interview the investor - known as the Sage of Omaha for his incredible moneymaking skills - warned Bitcoin backers face disaster.

"In terms of cryptocurrencies, generally, I can say with almost certainty that they will come to a bad ending", he said.

The Chairman and CEO of Berkshire Hathaway refused to take a short position on Bitcoin.

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"We don't own any, we're not short any, we'll never have a position in them," he said.

"I get into enough trouble with things I think I know something about", he said.

Buffett is not the only consumer looking to keep things old-fashioned.

In October last year Motorola revived its iconic RAZR phone, joining forces with British firm, Binatone, to create the Binatone Blade.

Like the RAZR, the Binatone Blade features a flip-open screen, but costs just US$66 – significantly cheaper than the RAZR, which cost US$600.

Speaking to CBS Philadelphia in November last year, Darren Zygadlo, creator of onecutreviews.com, suggests that "dumbphones" are set for a comeback.

While these "dumbphones" only have basic features, he he predicts that they could soon be the next big trend - and buyers are already beginning to snap them up.

Experts claim that one of the biggest draws of these basic phones is the nostalgia associated with them, as well as the significantly lower price tag than smartphones.

People are also finding they don't need all the functionalities offered by more expensive smartphones, and would rather have the simplicity of a paired-back device.

Zygadlo said: "I think there's a lot to be said for a product that makes you nostalgic.

"We've hit a point where we can pretty much do everything with these phones and I think some people are finding themselves saying, 'What do I need all that for?'"

In February, Nokia released a new version of the 3310 phone, 17 years after the original version was launched.

The retro device features a month long standby, the much-loved game, Snake, and costs just US$66.

French online shop Lekki, which sells a range of vintage, revamped mobile phones, claims simplicity is the way forward.