yes u can do that...usually, in a normal phone u wont be able to send text msges via Bluetooth..but there are softwares that allow u to send SMS via blue tooth. for more info...u can see this site..
http://www.bluejackq.comand another site that provides the software is
http://www.mobiluck.comonce u install the mobiluck in ur phone and turn it ON..whenever a bluetooth activated device is nearby...it will give a msg '1 device detected'
but the working depends on the phone-to-phone...i use NOKIA 7610 when i tested it on my friends phones...here are the result
on a Series 40 phone---> i was able to send him a msg directly like SMS..without asking permission unlike a normal bluetooth connection
on NOKIA 6230 ---> it showed him a msg 'Accept connection from sg-GOD?' when he pressed 'Accept' , i was able to send him the msg. Rejected and showed 'sending failed' when he pressed reject.
other phones like LG ----> it reached their phone as 'msg.txt' file but no 'Open' option was there...they cudn't do anything with that..rather than deleting it..
Actually as @fridgeuk told....therez no fun in this software..mayy be its just designed to annoy ppl.may be one point is that u can send a free Bluetooth msg to ur friend if he/she is near in abt 10-15metres (coz some of the operators charge 0.5cents for a single SMS)