Can I update firmware and/or baseband after unlocking the iPhone 4?

[Palaksi]

I have iPhone 3G with me, and I want to upgrade the firmware of that phone to 4.2.1. I have unlocked my iPhone by jailbreaking. So I want to know if there will be any problem to my [hone? Also, if I update the baseband will there be any issues??

[teenQ]

What model phone do you have? If you have a newer iPhone 3G / 3GS usually are the ones with model numbers beginning with MC, then if you upgrade to iOS 4.2.1 the jailbreak that you have performed will be Tethered. Tethered means that every time you switch off your phone, for restarting it in the unlock mode, you will have to plug it to a PC and jailbreak it again which becomes annoying. Also, please do not update the baseband to 06.15.00 also. Apple has built-in a new baseband version check that will just stop your phone from booting and starting up if the version isn’t installed. Also, you cannot downgrade the baseband if at all you install it.

[Beothuk]

Yeah, be vary of these, this is a serious thing and will severely hamper your phone. If you upgrade the firmware to 06.15.00, and then try to upgrade or restore iOS 4.2.1 or any future releases, you cannot use your iPhone! You can only downgrade it to 4.1 version. So, just wait until some solution of this problem is found out. So, if anyone tells you it will solve your problems by upgrading just don’t install it as of yet.

[Odalis]

There is a easy solution for it:
If you are on 4.1 just download 4.1ipsw
1: Install Redsn0w, and select 4.1 ipsw. Wait for load up
2: Next click on option next to ‘install Cydia’ and install iPad baseband.
3: click next and wait for finish
4: Now once restarted run Cydia and unlock the phone.
I have tested this on 5 3G/3Gs iPhones, and it is working fine.

[Common]

If you upgrade it to 06.15.00, you do this at your own risk! Please understand the consequences of updating to it:
• You cannot downgrade your phone back down from 06.15, and cannot hide it from Apple. You will also be voiding warranty for the phone.
• The main thing is that you cannot use update future baseband version if you install this. Even if it comes out with a critical fix, you cannot update it if it remains down in the 05.xx sequence
• You cannot even use the stock firmware back if you get this one. You will only use the custom IPSWs not the real ones.

[Apple.Mac.Rocker]

it's too easy for Apple to chunk all new iOS firmware for iPhones with 06.15.00 BASEBAND. The only solution for those who updated to 06.15.00 BASEBAND is to rely on custom farewell only.