A new report from ABI Research finds that Symbian remains the “smartphone” operating system market leader. The ABI study examines the pros and cons of the major smartphone operating systems, including the big three: Symbian, Windows Mobile, and embedded Linux.

According to Philip Solis, senior analyst and author of the study, Symbian’s chief advantages are that it is easy to build applications for, and that it has a large developer community. Disadvantages are that Symbian is primarily limited to Nokia handsets, and its market is concentrated in “GSM-heavy” regions, Solis says.

A key advantage of Windows Mobile, according to Solis, is its enterprise focus. For example, it interfaces well with Microsoft Exchange Server, which is widely deployed in businesses. On the negative side, Solis says, “Microsoft likes to control as much as possible of its end-users’ experience, and so do operators, who want to fully customize the user interface.”

The third key contender — considered by some to be a “wild card,” according to Solis — is Linux. “In its favor, it’s highly customizable, and inexpensive,” Solis writes. “But while it has been embraced by market leaders in Asia, it’s still an unknown quantity elsewhere.”

Last year ABI suggested that the Symbian would lose market share over the next five years, possibly falling below 50 percent. Solis stands by that forecast: “Symbian is still by far the market leader, but more Windows Mobile phones are reaching the market,” he says.

A new variable, since last year’s report by ABI, is PalmSource’s plan to convert Palm OS into a middleware layer on top of Linux for use on mobile phones. “We are bullish about the prospects for a rebranded Palm user interface running over Linux (alongside many other Linux OS solutions) taking some of Symbian’s market share,” said Solis.

For its part, market analyst IDC projected earlier this year that Symbian’s market share would actually increase by 2009 from the current 55.9 percent to around 60 percent.

However, neither ABI nor IDC seems to have factored in the potential impact of the Windows Mobile Treo smartphone announced last month by Palm, Microsoft, and Verizon.

The new ABI Research study, “Smartphones: The Market for Smartphones and Smartphone Operating Systems,” examines the smartphone’s role, combining communications and computing as an extension of the PC, the Internet, and the corporate intranet. The report also discusses strategies of carriers to attract and retain customers looking for these high-end devices.