How to upgrade my jailbroken/unlocked iPhone 3g from 3.0 to newer iOS, jailbroken and unlocked?

I have the same phone; using it with T-Mobile. OS 4.1, modem firmware [baseband] 05.12.01. [BTW, that's a version number, not a date] You can upgrade to the latest, 4.2.1, but doing so while keeping your unlock will involve upgrading your phone to the iPad modem firmware, which is a one-way upgrade and makes me a little nervous. I feel like I've read equal numbers of "worked for me" and "GPS doesn't work anymore!' If you want to go that route, http://www.iclarified.com/entry/index.php?enid=12949 will walk you through it. Their caveats:There is no way to come back down from 06.15, and there’s no hiding the baseband version from Apple. You’ll be voiding your warranty in a very obvious way.If some future baseband comes out with a critical fix, you won’t be able to update to it if it remains down in the 05.xx sequence (then again, you wouldn’t update to it if you wanted to keep your unlock anyway).Starting with FW 4.2.1 if you have 06.15 on your iPhone you won’t ever be able to restore to stock firmware (it will fail). You’ll need to only restore to custom IPSWs (then again, if you’re unlocker you should already be doing that).There are reports that 06.15 may disable your GPS. The iPhone Dev-Team is currently working on a fix. In my opinion, the preferable option is to go as high as you can in iOS versions without upgrading the modem firmware. That requires one to build a custom ipsw file, but the premiere tool to do that, PwnageTool, runs only on the Mac. Fortunately, you can download a http://www.iphoneheat.com/2010/10/download-custom-ios-4-1-firmware-ipsw/ that will update your 3G to 4.1 while preserving its current modem firmware. You'd use iTunes to restore your phone to that custom firmware [shift-click on the "Restore" button to bring up a dialog which allows you to choose a specific firmware file]. A purported Windows equivalent to PwnageTool is http://ih8sn0w.com/index.php/products/view/sn0wbreeze.snow. Here's a http://ih8sn0wforums.com/viewtopic.php?f=56&t=3545&sid=584478833440fd8f8339aadacdff8afa that does what you want to do. It's much tweakier than PwnageTool, and if I remember correctly I had problems during the latter parts of that method. To the best of my recollection, my iPhone is running a firmware I built with sn0wbreeze and then restored to the phone using iTunes. I've got Macs at home, but at the time PwnageTool had a bug where it would go off into space for hours trying to use Spotlight to search for the firmware file that was sitting right next to it in the same directory. 4.1 is better than 4.0 was; there's a jailbreak app that lets you turn off multitasking, which helped. 3.1.3 was faster, as I recall. I mostly upgraded for app compatibility. I do see, every now and then, a spontaneous reboot, usually while trying to launch BiteSMS. I'd say that happens maybe twice a month.

On preview I see you've answered your question, but since this is typed... Jailbreak: http://www.iclarified.com/entry/index.php?enid=9202 Spirit method won't require you to restore your phone again. I've never used it, but it looks a lot like the greenp0ison method I used on my iPad. http://www.iclarified.com/entry/index.php?enid=7443 RedSnow will involve another restore. It's operation is similar to sn0wbreeze above. If you've upgraded to a factory 3.1.3 ipsw, you've upgraded your baseband to 05.12.01, so the major advantage of using sn0wbreeze [preserve your baseband] is moot. The RedSnow process is very straightforward, as well. Unlock: http://www.redmondpie.com/unlock-iphone-3.1.3-3g-3gs-with-ultrasn0w/ There is only one game in town for carrier unlocking, UltraSnow. The current release of UltraSnow will unlock basebands 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00.

My household has a jailbroken 3G still running 3.1.2 (for exactly those performance reasons). By far the most effective fix for sluggishness on the 3G is to force-free some memory using the skull-and-crossbones icon in SBSettings. Do that two times right in a row, and the improvement is even better.

Thanks! This was all super-helpful!

spike - yeah I wondered about that. I'veheard mixed reports about 4.x on the 3g. Right now, though, my phone is crazy sluggish, due, I'm guessing, to too much apps/data/jaibreak crap, etc. So it seems like the best thing to do is clean it all up and start again. But a lot of the apps I love no longer run in iOS 3.0, so my thought has been that if I want to re-install, I'd probably be best to go to 4.x.

I think I answered all my own questions. I jailbroke the phone using jailbreakme.com, which seems to have worked okay (and so crazy easy to do). Thanks all for the help!!

Okay. My phone is now in a factory-restored state, running iOS 3.1.3. I now need to jailbreak and unlock it. Does anyone out there have recommendations on what is the best tool to use for this? (I am running windows 7, and a recent version of iTunes...)

One more Q: If I upgrade to 3.1.3, using the file from Oktober's link, using "shift-click" in itunes - do I need to do anything special to preserve the baseband? Or do I only have to worry about that in later versions of iOS?

(Duh - just found the answer to my fist question: "How do I upgrade to 3.1.3?" It is right there in Oktober's link: "you can shift-click (PC) or option-click (Mac) the Restore or Update buttons in iTunes")