STan:

Tried talking to the girl but she insist they are just normal friend. But to SMS him 1000+ messages a month is not normal. She even ask my son to change classes on sat to go to her school event to keep her company. Talk to her and even tell her my son got ADHD and is easily distracted with phone SMS in class also no use. If she listen to reason I don't have to air my frustration here.

honestly i think 1000+ smses a month may be quite normal for teenagers and is your son supposed to use his phone during class in the first place. besides he can always put his phone on silent mode/switch off during lessons so he would not be distracted by it at all.