I don't think anyone will be surprised by this, but watch out for Linux (am I five years too late?). According to market-research company IMS Research, the role of Linux in mobile systems will maintain a steady growth path. In addition, an increasing number of companies are announcing plans to develop Linux platforms. Admittedly, Linux phones still represent a small segment of the overall handset market.
IMS claims that Linux is uniquely positioned in the operating system (OS) space with implementations in both the smartphone and feature phone segments. This differs from competitive OSs, such as Symbian, Windows Mobile, and Palm, which have placed more emphasis smartphones.
Benefits of Linux as a mobile OS include its small kernel size, open source, and low (no) cost. I'm sure some of you are ready to debate some of these issues (particularly the low or no cost), but I can still make an argument for all the stated features.
With all this in mind, where is Linux headed? The guess here is that it will continue to increase market share, particularly for systems coming from Asia. As designers become more comfortable with the technology and the tools become more productive, there's no telling where it can go.