Ranking cell phone companies is a tough thing to do. Some of these companies have a bunch of popular handsets, whilst others have just one or two yet manage to sell as many or more. Rank the companies by cumulative sales across all of their lines and the results will swing one way; rank them model-by-model, and they might look completely different.

Such is the case with the iPhone, according to the latest numbers from The Nielsen Company. While RIM’s marketshare with their BlackBerry line is still nearly double that of Apple’s, the iPhone has now surpassed everything else to become the most popular phone in the US.

The iPhone’s lead is fairly tight, coming in at 4.0% of all mobile phone owners while the BlackBerry 8300 series follows closely behind at 3.7%. The rest of the list is made up primarily of feature phones, outside of appearances by the BlackBerry Storm and the BlackBerry 8100 series in 7th and 10th respectively. As the iPhone 3GS doesn’t make an individual appearance on the list, we’re assuming that they’ve combined the 3G and 3GS into one product line.

A few more interesting tidbits gleaned from the Nielsen report:

• The most popular reason people pick pre-paid phones isn’t because the lack of contract — that’s actually #4 — but because the plans are more straightforward. It’s followed by “No monthly bills” and “Emergency use only”.
• 21% of households now use mobile phones only, with no land line to call their own. This is up from 15% in 2006
• 15% of households now own at least one smartphone

Crunch Network: TechCrunch obsessively profiling and reviewing new Internet products and companies