For one thing: he should NOT be giving out his cell phone number (or e-mail addresses, if he has an e-mail) to ANYONE... unless he asks you first.
And the reason is: (I work at a school), everyday... I see kids who go around giving out their cell phone number to anyone who asks. Then, that person gives out their cell phone number to others too, (without asking first) and then before you know it, SO many people, have your cell phone number, and it will be people you do not even know, and people who you would NOT want, to have your number. And then, others start texting you, or calling you... and yes, it can get harassing.
And inappropriate.
So, if a kid, is more selective about giving out their cell phone number, or does NOT give it out, period (unless they ask you first), then, no one can "text" you, much less... icky pushy inappropriate kids.
At school, I even see kids giving out their Mom's cell phone number... to other kids. Who knows why. But the parents don't even know their kids are doing this. And before you know it, even the parents are getting calls or texts... too. From, kids.
For our daughter who is in middle school, our rule is DO NOT GIVE OUT your cell phone number, to ANYONE, unless you ask me, first. And she follows our rules. She knows, the potential trouble... of giving out your cell phone number. AND, if/when she does give out her number, after asking us first, she TELLS her friends "YOU CANNOT GIVE OUT MY NUMBER to anyone else, without my or my Mom's permission...it is private....." and they listen.
Your son, needs to learn how to stand up for himself.
And how to protect his personal information (ie: his cell phone number etc.) and how to jut speak up. To ANYONE that is pushy and aggressive.
And sometimes, you just have to tell the other kids "BACK off....I said no... do it."
And if you know the Mom of that girl, I would tell the Mom.
Those girls, are running all over him. Because they can, push him around.
Some girls are very very pushy and aggressive and, problem making.
And he has to learn, how to stand up for himself and just be firm.
My daughter is in 6th grade. Some of them are age appropriate. Some are not. Some of the girls, (and they all flock together), ARE this way... just over the top into boys and creating drama about it with others. So, the kids that do not like them, simply go and make friends with other, kids. NOT them.
The thing is, you don't have to be friends, with kids like that.
Is it your choice, too... who you choose to have as friends.
Or not.