Now that the 3.1 update has hit iTunes many will jump to download and install as soon as possible, however as the past has shown this is a bad idea if you are a jailbreaker or unlocker.
The 3.1 update includes an update to the modem software that removes over 50% of the commands. The less complex the software is, the less likely it is to find a hole to unlock it with.
What does this mean for you?
If you are using ultrasn0w or purplera1n for your unlock, updating your phone to 3.1 could permanently lock your phone back to its provider’s network. There is no downgrading, there is no undoing the 3.1 install, so proceed with caution.
As with every update, wait until the dev team (http://blog.iphone-dev.org) has released the tools to safely install without updating the modem software. This will ensure that your phone remains unlockable, and that at the time you update, a jailbreak is available for you.
You have been warned
Just FYI, you should update this post: http://appadvice.com/appnn/2009/09/start-downloading-itunes-9-now-its-a-big-improvement/
and remove the bottom recommendation of getting 3.1
Why? Unlockers are in the minority not the majority of iPhone users?
I have a question: If i’m a jailbreaker (not an unlocker) can i download the 3.1 firmware without danger of not being able to jailbreak again later? Or is this warning simply for people who want to use their phones with a different service provider?
That’s a loaded question. If you are using a 3GS then you need to make sure you get your ecid dumps before updating, and again you won’t have a jailbreak for 3.1 until tools are released from the dev team, all of your jailbreak apps will be deleted when you update.
If you are using a 3G/2G then you can safely update to 3.1 and a jailbreak will be available in the future, but again not until tools are released, and you will lose all of your jailbreak apps during the jailbreak.
Hope this helps