I am a convert! After reading The Warlock's posts, and trying it out for myself, I am starting to beleive that the "shout first" method appears to be most consistent with the rules of spellcasting (and ability use in general), including spell secrecy. In addition, I now also realize why the simultaneous effect rule may not apply to voluntary spells and abilities, only to triggered events.
Yep "shout first", "declare first" without saying what spell you have. Like I said before a simple "do you want to use your charm" would be a good idea before casting your spell. Of course this might lead to bluffing but hey that life.