I thought maybe this would be something in the Polyamory FAQ in the sidebar, but that link is broken.

I've been fantasizing for a long time about MFM, watching a guy fuck my wife, or hearing about her getting laid/getting texts (much like I've been seeing on /r/hotwife since following). I'm curious how others first brought the idea up to their wives. I think the obvious short answer is, "In a healthy relationship, you would just talk openly about it," but I think I'd benefit from hearing about others' obstacles, butterflies, excitement, snags and breakthroughs, and so on. I think there's certainly some potential for shock when a guy first tells his wife that he wants her to have sex with other men.