Not sure if you've read the DJ Bible or not, but there is a link on there that explains exactly how to start spicy convos! The key being talking about sex. Although double entendres and subtle (clever, not immature) innuendos work too dude.
But something I tried over the phone with one girl, was saying that in my Psychology class, my female teacher showed me a poll that recorded 60% of women saying they prefer sex on top, being able to control their own orgasms and all that....this was pure bullsh*t made up by me of course, no actual poll, but I am taking a Psychology class! = P The conversation sparked into life and it was the beginning of some of my most interesting exchanges with a girl.
If she takes the bait, thats a pretty good sign....you can end the convo with, "So if you and I had sex, would it be amazing? = D" Anything other than, "What..?" is a good answer! Those are my experiences.