Just now rooted my AT&T Samsung Galaxy S II phone using heimdall on my Mac. Instructions: http://forum.xda-developers.com/showthread.php?p=18576627#post18576627 (11:30 PM)
Was not able to copy the file (zImage) of Siyah into the phone’s card using Mac Terminal. Wasted a lot of time on this. Decided to go ahead and copy the file to the phone’s /download folder for following instructions 3d in the above link.
Installing ClockWorkRecoveryMod is completed (12:23 AM)
Tried Ultimatum and SHOStock2. Ultimatum crashes the android.com.phone service. Reverted to backup (05/03/2012 : 12:20 AM)