L.U.
E. - Yes, the boy is in the wrong but your daughter is just as much as him. "your good Christian daughter" wasn't saying anything back to him? Wasn't laughing or giggling? The boy is only 13, I don't think they are even smart enough at that age to "seduce" they just are constantly horny and will go with whoever is willing. Right now, your daughter is willing. Was she embarassed about what was being said or embarassed that she was caught listening?
Yes, I think your husband SHOULD have a talk with that boy. I don't know if my husband would be a good "talker" but he would definetly get his point accross. :) Someone else said to have the parents over and repeat word for word, that sounds like a mighty uncomfortable and good idea.
I think that it is more likely than not that your daughter is enjoying the attention that she is getting from this bad boy. She already knows that he has some kind of history with another girl yet continues to talk and call him. Your daughter has the power here, she just needs to hang up the phone.
L.