If you own a s60 v2 phone(5320 is s60v3), then you can use "Bluetooth Messenger" to send messages via bluetooth to your friends, but they too will need s60v2 phone with the software installed. And yes, the copy-paste method in notes, is a good one to send message, but is a bit pain doing it each time.
You can get this software easily by a google search.
For s60v3, try searching for similar app. I will search and give you the link if I find one.
For java, I don't think there is any such bluetooth messenger.
Also instead of messaging a unknown girl, you can use this great software for sharing ANS in a classroom during exams.