Ok, I pulled up the menu list for an i576. I cannot vouch that it is the same there that it is here.
First, both devices must be set to Direct talk. to do this, press the menu button & select Direct Talk. Select GO TO DIRECT TALK. After a few seconds, your channel & code will appear on your screen. To exit Direct Talk mode, press the menu key again, and select DT OPTIONS, select EXIT DIRECT TALK.

There is actually quite a bit of info. If you like, I can send you a PDF of the users manual. Or, if you have it, and its the same one as I am looking at, its on page 67. If you want the PDF, let me know, I'll email it to you today.