I found out, kinda!! Its called bluejacking. Its not exactly like sending an actual text message, its just a short msg that pops up on the person's screen, depending on what model phone you have you might know who it comes from and you might not. I tested it with my friend who has a E530 and my bluetooth name popped up but I did it to my bf (he sits across the office from me) and he was freaking out, I could see his poor little face all confused as the messages popped up on his screen. I sent him '7 days'!!!!
Anywho, what you do is create a contact with a number like 0000 or whatever then type your message in the name section then send the contact card via bluetooth and only the name will appear on the other persons phone