People used to buy personal computers every year or two. Remember? That was when the industry was quickly moving from 286 to 386 to 486 to Pentium processors. Concurrently, Microsoft was flying through versions of DOS and Windows. Also, sophistication of productivity and gaming software was growing rapidly.

Hard drive space, along RAM amounts and speed were skyrocketing.

If your computer was 18 months old, it was MUCH slower than the latest model.

Over the years, things peaked and plateaued. People bought PCs less frequently. There were fewer reasons to upgrade. These days, I’d argue the magic number of computer shoppers is 4-5 years: e.g. the computer you bought three years ago is plenty capable to doing the same work — for the majority of consumers, Web and media-based — today.

Well, last week, JD Power and Associates released a study that found that we are keeping our smart phones longer than in the past.

The average consumer doesn’t upgrade their phone for 20.5 months before buying a new one.

That’s a 17 percent increase over a year ago.

JD Power says this is mostly happening because of the struggling economy.

But I have another thought: What if smart phones are moving towards a plateau, like PCs did?

I mean, the screens are huge and bright and high definition; the storage is ample; most apps created for platforms like the iPhone and Android phones work well; photos and video captured with today’s smart phones are generally very high quality.

Smart phones are a fast-maturing category of consumer electronics.

It’s also true that this is also the high-tech category seeing the most investment in research and development right now. But consumers are voting with their dollars, and it appears people are seeing less need to upgrade their iPhone 4 and their Android 2.1 devices.

This may well be the beginning of a leveling off of smart phone sales growth.