I started going through that with my oldest son when he was about 5th/6th grade. Those girls can be REALLY persistent.
It was basically the same thing -- a girl calling here 2 or 3 times a night and then friends of the girl calling to pass on messages or do the "she likes you, do you like her" thing.
The problem was, he actually had very little interest in girls then. The girls just seem so much more mature than the boys at that age. The result was, he really didn't treat them very nicely. He would be rude on the phone..hang up on them, etc etc etc. We had to have several discussions on how he didn't have to be a boyfriend, but he did have to treat girls nicely and with respect no matter what. I also said that I was always more than willing to be his excuse "I"m sorry, but my Mom says I can't talk on the phone tonight. I'll see you in school tomorrow."
Now that he is in High School, I worry much more.