Is this what your looking for.. ?
http://forum.xda-developers.com/showthread.php?t=334759
No offence but you should try to google (also search the forum) before you start a thread. I dont even use ATT or an 8525, all I did was google "disabling Push-to-Talk button 8525" and I came up with the above on the first page of results.
Good luck though, I hope it helps.