Here are the steps I took for unlocking from a MacBook Pro. These are
paraphrased from: http://www.freeiphoneunlock.com/guide/

   NB!!! There has been talk recently of a firmware upgrade that will
   "break" present non-AT&T activators and unlocks. See the link above
   and follow discussions on forums such as Engadget.com for the
   latest news.

   This guide was up to date at the time I last unlocked my
   iPhone. Procedures may have changed, been simplified and improved
   since then.


0. Read and make sure you understand all the steps before
   starting. Don't mix and play software until the unLock works. Read
   and understand all the documentation that comes with the files you
   download to perform this unlock.

   Unpack your iPhone, plug it into the USB port of your Mac with the
   provided cable to start charging it and for initial
   communications. 

   Make a directory named something like "iPhone" somewhere convenient
   on your Mac in which to download the various files needed. (In a
   shell, cd to that directory before logging into the iPhone.)

1. Make sure your iPhone firmware is version 1.02 and iTunes is 7.4.

   (If it's not, you will have to upgrade the firmware with
   iTunes. This involves going a couple of steps into the iTunes
   activation process and then back out until iTunes offers to Restore
   the phone to firmware 1.02.)

2. Get iNdependence and then get the appropriate iPhone firmware from
   Apple. (See the iNdependence README file)

   http://iphone.fiveforty.net/wiki/index.php/INdependence

3. Activate and jailbreak the iPhone with iIndependence

4. Make sure your Modem Firmware is 03.14.08_G (Settings > General >
   About > Version) 

5. Get AppTapp Installer, unpack and install Installer on the iPhone

   http://iphone.nullriver.com/beta/

6. Make sure your iPhone is connected to the Internet. Get its IP
   address from Settings > General > WiFi > [basestation] > [10.0.1.4]

7. Use Installer (on the iPhone) to install (in this order):

   - Community Sources
   - BSD Subsystem (might take some minutes)
   - OpenSSH

   Installer will install these over the WiFi connection. 

   Installing "Community Sources" will bring up a list of available
   resources, among them OpenSSH and BSD Subsystem

8. You can now log in on your iPhone from a shell on your Mac with
   "ssh root@10.0.1.4" (user: root password:dottie) It takes 30-40
   seconds for the iPhone to respond the first time as it generates
   keys. 

   Log in to ensure that you have a connection over which to move the
   files below. 

9. Get these files onto your Mac like this:

   curl -O http://www.freeiphoneunlock.com/unlock/files/iUnlock
   curl -O http://www.freeiphoneunlock.com/unlock/files/nor
   curl -O http://www.freeiphoneunlock.com/unlock/files/ICE03.14.08_G.fls
   curl -O http://www.freeiphoneunlock.com/hardware/minicom
   curl -O http://www.freeiphoneunlock.com/hardware/minirc.dfl
   curl -O http://www.freeiphoneunlock.com/hardware/bbupdater

10. Copy the following files to /usr/bin on the iPhone with scp.

   - iUnlock
   - ICE03.14.08_G.fls
   - nor
   - minicom
   - bbupdater

    For example ("khadija $" is the prompt in the shell on my Mac):

    khadija $scp iUnlock root@10.0.1.4:/usr/bin/
    root@10.0.1.4's password: 
    iUnlock                     100%   19KB  19.3KB/s   00:00    
    khadija $


11. Make a folder under /usr/ called local/etc

    I'm logged in on the iPhone:

     # pwd
     /usr
     # mkdir local
     # mkdir local/etc
     # 

12. Upload minirc.dfl to /usr/local/etc/

     khadija $scp minirc.dfl root@10.0.1.4:/usr/local/etc/
     root@10.0.1.4's password: 
     minirc.dfl                    100%  104     0.1KB/s   00:00    
     khadija $

13. Log in to the iPhone and run the following commands:

    # cd /usr/bin 
    # chmod +x iUnlock
    # launchctl unload -w /System/Library/LaunchDaemons/com.apple.CommCenter.plist 
    # 
    # iUnlock ICE03.14.08_G.fls nor
    iUnlock v42.PROPER -- Copyright 2007 The dev team


    Credits: Daeken, Darkmen, guest184, gray, iZsh, pytey, roxfan, Sam, uns, Zappaz, Zf
    
    * Leet Hax not for commercial uses
      Punishment: Monkeys coming out of your ass Bruce Almighty style.
    
    Sending Begin Secpack command
    Sending Erase command
    Waiting For Erase Completion...
    00%
    00%
    [Wait a while - usually around 20 minutes.]
    ........
    95%
    Sending End Secpack command
    Validating the write command
    FW are equal!
    Completed.
    Enjoy!
    # 

14. Remove the AT&T SIM and install your own.

15. Then:

    # chmod +x bbupdater 
    # bbupdater -v      
    Resetting target...
    pinging the baseband...
    issuing +xgendata...
        firmware: DEV_ICE_MODEM_03.14.08_G
     eep version: EEP_VERSION:207
    eep revision: EEP_REVISION:7
      bootloader: BOOTLOADER_VERSION:3.9_M3S2
    Done
    #     

16. Then run minicom: (you type the commands after the ">")

    # minicom

        Welcome to minicom 2.2
        
        OPTIONS: 
        Compiled on Jul 21 2007, 05:09:51.
        Port /dev/tty.baseband
        
                Press CTRL-A Z for help on special keys
                                                             
      > AT                                                   
        OK                                                   
      > AT+CLCK="PN",0,"00000000"                            
        OK
      > AT+CLCK="PN",2
        +CLCK: 0
        OK
     
      > [ctrl + A Z and choose "X" to reset and exit]

17. Now run:  

    # launchctl load -w /System/Library/LaunchDaemons/com.apple.CommCenter.plist


    SUCCESS!


This guide is up to date on Sept 15, 2007 for revisions see:
http://www.freeiphoneunlock.com/guide/