Android and Apple account for more than 90 percent of the surging smartphone market, and third place is being contested by BlackBerry and Microsoft's Windows Phone.
But phones using operating systems based on the open-source platforms Linux and Mozilla's Firefox will be hitting the market this year, most likely in emerging markets.
Among smartphone makers, "there is a consensus that there is room for a couple more operating systems," said Ramon Llamas, analyst with the research firm IDC.
"Maybe not globally, but in some markets which could be used as proving grounds."
An IDC survey showed Apple and Android accounted for 91.1 percent of all smartphones sold in 2012, but that new platforms are worth watching in a market with 46 percent growth last year.
The Mozilla Foundation, developer of the Firefox browser and a new mobile operating system, claims to have 17 operators on board and plans Firefox OS phones in Brazil, Colombia, Hungary, Mexico, Montenegro, Poland, Serbia, Spain and Venezuela.
The key player being watched, however, is Samsung, which is the biggest smartphone maker with some 40 percent of all Android phones but is planning new devices using Tizen, an operating system based on Linux.
The Tizen Association, which also includes France's Orange, Japan's NTT DoCoMo, China's Huawei and US-based Intel, say the firms "view openness as a key to raising the bar for user experience."
Some analysts were surprised by Samsung's move, saying it's not clear if the South Korean giant is trying to distance itself from Google and Android, which is a free operating system but offers advertising possibilities to the Silicon Valley firm.
"I wonder about Samsung's motivation," said Roger Kay of Endpoint Technologies.
"To get out from Google's control might be part of it, but I'm not sure how rational that is. The partnership has been very fruitful for both companies, and it's hard to see where the negatives are."
But Aapo Markkanen, an analyst with ABI Research, said Samsung is trying to break free from Google and that Tizen could be the key for that.
"All signs are pointing to Samsung trying to pull off a Great OS Escape within the next year or two," Markkanen said in a blog post, adding that the platform "will be given a kick start with the software and service portfolio that Samsung has accumulated" along with "Samsung's gargantuan marketing budget."
Other Linux phone systems are also readying their entry.
Ubuntu, a Linux-based operating system promoted by British software firm Canonical, expects to have phones ready later this year. And Sailfish, another Linux variant from Finnish-based Jolla Mobile, has released its program for developers.
Analysts say smartphone makers are seeking to mimic the success of Apple by controlling both the hardware and software "ecosystem."
"We are seeing more desire to control the whole user experience," said Gerry Purdy, analyst and consultant with the firm Mobile Trax.
A major challenge for any new platform, however, will be developing the applications that make up the ecosystem. These are key attractions for users of the iPhone and Android devices.
Although some apps can be developed across platforms using HTML5, a programming language that can be adapted for different devices, analysts say these are inferior to "native" apps developed for a specific platform,
"You can provide a reasonable experience with HTML5 and the browser, but the native app is smoother, cleaner and more natural," Purdy said. "It's pretty obvious when you watch them side by side."
Even a powerful firm like Samsung will have a hard time putting together an app ecosystem that can compete with Apple's App Store and Google Play.
"There is some open space, but putting together an entire ecosystem and doing that where there are established incumbents is a pretty iffy proposition," Kay said.
Because of these obstacles, Llamas said progress for any new system will be "long and slow."
"None of these things will happen overnight. There has to be time for gestation, reception and evangelization. And picking the markets will be important," he added.