Apple Inc. reported its fastest quarterly revenue growth in more than three years, easily topping Wall Street estimates, after demand picked up for the iPhone and products in China.

Apple's best revenue growth in three years failed to impress, with shares down about 1% in volatile trading on Friday, as investors questioned whether a tariff-driven surge in iPhone sales would last.

Apple has sold over 3 billion iPhones since its first smartphone in 2007. Samsung got there first, but there are some caveats to consider.