The iPhone 4 gets better with age

Like a fine wine or stinky cheese, Apple’s iPhone 4 seems to get better with age.

Apple just reported record iPhone shipments — 20.3 million units — for a year-old device. That’s up 142% year-over year from its launch quarter. (Actually, some of those phones may even be the iPhone 3GS, which is now almost two years old.)

Here’s Apple’s ever-increasing iPhone unit sales tally since the iPhone 4 went on sale last June:

• June 2010: 8.4 million
• September 2010: 14.1 million
• December 2010: 16.2 million
• March 2011: 18.6 million
• June 2011: 20.3 million

Why is this happening?

For one, the iPhone 4 is still the best overall phone on the market. Sure, other phones may be superior on a feature-by-feature basis, but when you look at the complete package, nothing tops the iPhone 4. So for people who just need a phone, and not necessarily the absolute newest one in the world, the iPhone 4 is still their best bet.

Apple also continues to add new carrier partners. And the white iPhone 4 launch probably helped. And overall interest in smartphones continues to grow rapidly, too. This all adds up to progressively larger sales for Apple.

And that’s how a year-old phone is Apple’s best-selling product.