Colleagues and friends of mine have published a great introductory book on OSGi. Its called "Die OSGi Service Platform -Eine Einführung mit Eclipse Equinox". Its completely written in German (but don't be afraid, they told me an English version is somewhere in the pipe) and the first book on OSGi on the planet. Wow. Make sure you get a copy and learn about OSGi. I can just highly recommend to read this great book!
German OSGi Book