iPhone 2G, 3G, 3GS users can now safely
update to 3.1.2 firmware without
updating the baseband (for unlock). If you are not the one to download
all the various files and just want the ultimate result, these files are
waiting for you to download! If you rather want to start from scratch,
download Pwnage 3.1.4 tool for Mac.

• Caution
  #1 : A restore is going to wipe the iPhone clean. Hence, please
  backup your iPhone using iTunes and then proceed.
  

More
info about these custom firmware
files :

• Has
  factory boot logos (Apple and restore cable),
  
• Only Cydia, No Icy
  
• Preserved Unlock baseband
  (that is the whole point of a custom firmware, right?!)
  
• Activated/Not Activated (Check the files carefully)
  

Prerequisite
(recommended) :
If your iPhone is already jailbroken at the current firmware (3.0,
3.0.1, 3.1), it will be a hassle free upgrade! Restore mode will work
just fine with already jailbroken iPhones.
Step 1.1) Download Files for iPhone 3GS (Please read the
following carefully)

• Download the following files ONLY if you have
  an Official iPhone contract
  with your cell carrier (ATT and
  others….)<blockquote>
  
• iPhone
  3GS 3.1.2 Custom Firmware Not Activated Official Carriers Part 1
  
• iPhone
  3GS 3.1.2 Custom Firmware Not Activated Official Carriers Part 2
  </blockquote>
  

OR

• Download the following files ONLY if you don’t
  have an iPhone contract (T-Mobile and others…)<blockquote>
  
• iPhone
  3GS 3.1.2 Custom Firmware Activated for Other Carriers Part 1
  
• iPhone
  3GS 3.1.2 Custom Firmware Activated for Other Carriers Part 2
  </blockquote>
  

Step 1.2) Download Files for iPhone 3G (Please read the following carefully)

• Download the following files ONLY
  if you have an Official iPhone contract with your cell
  carrier (ATT and others….)<blockquote>
  
• iPhone
  3G 3.1.2 Custom Firmware Not Activated Official Carriers Part 1
  
• iPhone
  3G 3.1.2 Custom Firmware Not Activated Official Carriers Part 2
  </blockquote>
  

OR

• Download the following files ONLY if you don’t
  have an iPhone contract (T-Mobile and others…)<blockquote>
  
• iPhone
  3G 3.1.2 Custom Firmware Activated for Other Carriers Part 1
  
• iPhone
  3G 3.1.2 Custom Firmware Activated for Other Carriers Part 2
  </blockquote>
  

Step 1.3) Download Files for iPhone
2G (Please read the following carefully)

• Download the following files ONLY
  if you have an Official iPhone contract with your cell
  carrier (ATT and others….)<blockquote>
  
• iPhone
  2G 3.1.2 Custom Firmware Not Activated Official Carriers Part 1
  
• iPhone
  2G 3.1.2 Custom Firmware Not Activated Official Carriers Part 2
  </blockquote>
  

OR

• Download the following files ONLY if you don’t
  have an iPhone contract (T-Mobile and others…)<blockquote>
  
• iPhone
  2G 3.1.2 Custom Firmware Activated for Other Carriers Part 1
  
• iPhone
  2G 3.1.2 Custom Firmware Activated for Other Carriers Part 2
  </blockquote>
  

Step 2) Join the downloaded files

• The files downloaded above have an
  extension .001 and .002. They need a special opensource (free) software
  HJSplit to join.<blockquote>
  
• Download HJSplit to join both the files – Link for Windows
  Computers here and Macs
  here.
  </blockquote>