Why would you? Android and iOS fight for worldwide domination, with no signs of slowing down. Both have extremely well-developed ecosystems that make sharing information across services and even across individual handsets a fairly simple, unified process. App development is strong, and OS updates are regular enough to give phone owners new party tricks to show off.
In the meantime, Microsoft is still reaching deep into its pockets to secure double-digit market share, and RIM hopes its upcoming BlackBerry OS 10 Hail Mary will win back its former fan stronghold.
This hardly seems the time to welcome newbies.
Why, then, with four operating systems competing for your attention, would anyone give a serious thought to a platform masterminded by the makers of a browser (Firefox), an OS from a hardware powerhouse that has an iffy software track record (Tizen maker Samsung), and a Linux OS that still hasn't gone mainstream for desktops despite years of effort?
The myth of choice
A four-horse race isn't very much fun, you might argue, and with BlackBerry still on the precipice, the three new OS hopefuls would offer some welcome variation from iOS, Android, and Windows Phone. Besides, customers always love choice, right?
In theory, yes, but just cast your mind back to 2009, when six major mobile operating systems vied for users: BlackBerry, Symbian, Windows Mobile, Palm WebOS, iPhone, and Android. There was competition, lots of it, but also complexity, uneven customer support, limited handset availability, and stunted app and OS development.
A year later, Microsoft's Windows Mobile OS and Palm's WebOS crumpled, and development of RIM's BlackBerry OS stuttered. Nokia still technically supports Symbian, but threw its weight behind Microsoft's Windows Phone reboot.
The mobile landscape consolidated for a number of reasons, one being that not enough customers supported each OS to keep its development well-funded. For one of these upstarts to succeed in today's cutthroat climate, it will need money, some extremely competitive hardware, and a truly new feature or approach.
Of the three, Firefox and Ubuntu have the deepest pools of committed developers, and Samsung has the money and muscle to force its vision onto a high-tech handset. Yet, there's no real hardware planned for any of the three until 2013 or 2014 (Firefox OS will be the first with a promised release in Brazil and other South American countries this year).
The Android factor
I'm not trying to argue that the status quo is and will remain solid enough to shut out disruptors. In fact, the iPhone and Android were two extremely successful disruptors in the pre-2007 mobile space.
Both iOS and Android offered a new paradigm -- intuitive navigation for iOS and openness for Android -- backed by massive companies with cavernous pockets and rock-solid hardware partnerships.
Though Samsung may be an exception, I don't see Firefox or Ubuntu being able to support such dramatic growth.
Just because I don't think the current landscape will support a fifth or sixth smartphone platform doesn't mean that one of those three won't achieve niche popularity.
Linux-loving mavericks and developers have been following Ubuntu and Firefox OS with enthusiasm, and these two could become a hotbed for some interesting experimentation in an open environment before the features or designs go mainstream.
There's also tremendous sales opportunity in developing nations where many people are converting from simple phones to smartphones. Pundits estimate about 1.7 billion smartphones sold in 2012, with the numbers rising year over year as smartphone penetration deepens in still-maturing markets.
Inexpensive hardware paired with simple open-source software could lure new smartphone users to unknown OS brands -- but compared with Apple and Google's clout, inroads would be minimal when taken in a global scale.
'The Web is the platform'
One thing we can glean from Tizen, Ubuntu, and Firefox is an emphasis on open-source code flexibility, and a reliance on HTML5 Web standards. Each leans on Web protocols that cross-cut device brands and proprietary code to store all data in the cloud, even while offline.
If there's a chance for a new OS breakthrough to take center stage the way that iOS and Android did, both RIM and Windows Phone will first have to fail and dry up just like WebOS. We'll find out how they'll do soon enough.
Until then, the front-runners have the resources to combat the up-and-comers, and any additional OS entrant would just add a lot of white noise.
Update, Thursday at 8:45am PT:Added clarification regarding Firefox OS' hardware plan.