Over the years I discovered that turning my thoughts outward toward another person pretty much eliminates the shyness, at least for the moment. I'm still desperately insecure at times, but I work in a library and I don't feel shy much at work because it's all about 'how can I help you?' Sometimes people are jerks, but for the most part they're pretty appreciative, and that feels wonderful. I think you are on the right track with volunteering.