New data out this week puts Apple’s iPhone at the number one spot on a Top 10 list of U.S. mobile phones, but they still lag in overall market share due to the competition having multiple models available.

Nielsen compiled the data on the Top 10 mobile phones in use from January through October, 2009 in the U.S., which gives Apple a 4% market share, according to Cnet News. Competitor RIM (Research in Motion) landed 6.3% with its Blackberry line and LG took 6.4%. Together, the Top 10 mobile phones in use account for only 20% of the total devices in use.

Apple’s rivals enjoy one competitive advantage in that both RIM and LG offer a number of different handsets compared to only two current variations of the iPhone, last year’s 3G model and this year’s 3GS. That said, Apple has been at the cell phone game far less than the competition and is only tied to one carrier, AT&T, instead of having the benefit of promotion from all U.S. carriers. LG is the number three mobile phone maker behind Nokia and Samsung.

The Nielsen report shows just how much the cell phone landscape has changed since the introduction of the iPhone in 2007. At that time, Motorola’s Razr was the cell phone to beat, while RIM was mostly a business-centric device for the enterprise. With the market constantly in flux, the mobile phone game is still wide open for the future and even ailing companies like Motorola have an opportunity to bounce back, as they have with their Android-powered Droid from Verizon.

There were an estimated 271 million U.S. cell phone users at the end of 2008 (approximately 88% of the U.S. population), so even a 1% share is big business. There’s also a growing trend for households to ditch their landline and use only cellular phones instead -- in the second quarter of 2009, 21% of households were doing just that, up from 18% a year ago.