A lot of headlines in recent days are focused on handset market share as research firms share their analyses of the fourth quarter. But it feels like the headlines are all over the place. Maybe it’s always this way and indicative of the many ways you can slice and dice the handset market.

Some things strike me as readily apparent and easily agreed upon. For example, most everyone knows Nokia is losing share, and the company in its own quarterly report estimated its mobile device market share at 31 percent, down from an estimated 35 percent in the fourth quarter of 2009 and up from an estimated 30 percent in the third quarter of 2010. Others put Nokia’s share at 31 percent in the fourth quarter (Strategy Analytics) or 30.8 percent (IDC). ABI Research estimates Nokia’s share slid marginally to 31.7 percent.

Nokia actually gave two preliminary market share estimates, one for mobile phones and another for “converged mobile devices.” It defines the phone category as Series 30 and 40-based devices ranging from basic phones focused on voice to devices with a number of additional functionalities, such as Internet connectivity, including services and accessories sold with them. The converged mobile device category refers to smartphones and mobile computers, including the services and accessories sold with them. Nokia’s estimated share of the converged mobile device market was 31 percent in the fourth quarter, so similar to the figure for the mobile device market but down almost 10 percent from the year-ago quarter.

One of the more striking reports about fourth-quarter data came from Canalys, which said Android shipments of smartphones hit 32.9 million, ahead of Nokia’s Symbian platform, which tallied 31 million worldwide. The Android figures include OMS and Tapas, and there’s controversy about whether those should be counted. At any rate, with regard to Nokia and Symbian, we’ll have to wait and see what Nokia CEO Stephen Elop reveals at that Feb. 11 investor conference in London.

Right now, it’s all clear as mud. In its assessment of the worldwide mobile phone market, IDC says that Apple “slipped to the number 5 position” despite a record quarter for unit shipments. It had an estimated 2.6 percent market share in the fourth quarter of 2009, but that improved to 4 percent by the end of the fourth quarter of 2010.

Strategy Analytics said some brands outperformed, such as Apple, while others underperformed such as LG and Nokia. In fact, Strategy states in its press release that Apple was a “star performer” during the quarter and again outgrew its major rivals. ABI Research seems to agree about Apple, headlining a release with: “Apple, RIM and HTC Win Big in 2010 Mobile Handset Race.” The text says “Apple’s iPhone 4 continues to capture a growing chunk of the smartphone market (4.2 percent).

All of these statements may be true depending on what’s being measured. I did find The NPD Group’s assessment quite interesting and don’t have any quibble with it. While ABI declares RIM a winner worldwide in 2010, NPD’s list of the top five handset models based on U.S. consumer purchases in the fourth quarter does not include a Nokia or a BlackBerry model. The firm identified the top purchased models as the Apple iPhone 4 at No. 1, followed by, in order, the Motorola Droid X, HTC Evo 4G, Apple iPhone 3GS and the Motorola Droid 2.

Adding fuel to the fire is this blog post from The Nielsen Company, which says when it comes to the installed base of U.S. mobile consumers who already own smartphones, it’s a three-way tie between BlackBerry, Apple iOS and Android. But  Nielsen goes on to say that analyzing the preferences of those who purchased a smartphone in the past six months paints a different picture – one in which Android is clearly in the lead with 43 percent of recent acquirers purchasing an Android device, compared with 26 percent for Apple iOS and 20 percent for BlackBerry.  

Don’t get me wrong. These reports are highly valuable, but everyone wants to know what’s going to happen this quarter and beyond, especially with the smartphone that begins with an “i” at Verizon. According to eMarketer, Apple will pass RIM as the leader in U.S. smartphone market in 2011, but not for long. (eMarketer bases its forecast on a meta-analysis of research estimates and methodologies from several firms that track the smartphone market.)

eMarketer says Google’s Android platform will overtake both Apple and RIM in 2012. It figures 31 percent of all smartphone users in 2012 will own an Android device and Apple’s share will hold steady at 30 percent. So, presumably, that leaves roughly 40 percent of the market for the others to fight over.

So what is it – Apple is gaining and Android is stealing market share from iOS? Various handset makers over the years have given more or less importance to market share, usually depending on whether their own standing is good or bad. Several sites are reporting this week on Asymco’s assessment that Apple’s share is under 5 percent of the market, but its share accounts for more than 50 percent of the profit. 

Without looking at specific numbers, we know Android is growing by leaps and bounds – how could it not? – and Apple’s iOS remains hugely popular. RIM is hanging in there, and it’s too early to say what Windows Phone 7 or HP’s Palm/webOS is going to do. Whatever happens, evaluating market shares next year at this time should be a whole lot more fun when you throw tablets into the mix.