Personally, I am amazed at how fast Odamex's been progressing. No matter what certain people say about it, Oda has pretty much beaten ZDaemon and Skulltag in terms of potential for competition. I thank you, fellow devs, for making this possible!
And, to answer your question,
this video should tell you how to do callvotes on Odamex. Or you could just watch it from the beginning to see how the whole thing works. :)