Despite the success of the Apple iPhone, Motorola can still claim to have the best-selling mobile phone in the United States. How long can the Razr hold onto the top spot? Can it fend off the competition forever? What is this simple phone's appeal?The NPD Group reported on handset sales in the U.S. recently. It showed that one-third of iPhone users switched from another carrier (and another handset) to adopt the smartphone from Apple. A little nugget was buried in that report. It shows that the Motorola Razr -- the original one, you know, from 2004 -- ranks as the No. 1 handset in the United States.

The top 5 are the Motorola Razr, the Apple iPhone, the BlackBerry Curve, the LG Chocolate, and the BlackBerry Pearl.

This befuddles me.

The Razr is ancient history in terms of design and features. It sold for $400 when brand new. Now it is often available for free. Perhaps the reason. Given the ever-worsening economic climate, I suppose it's no surprise that even in the era of the super-capable smartphone, people often choose with their wallets.

The Razr's reign can't -- and won't -- last forever. The question is, which handset will topple it?