Now you can upgrade and jailbreak iOS 5 on your iPhone 4 (GSM) at the same time while preserving your old baseband. Please note that this is a tethered jailbreak and as of the meantime there is currently no untethered jailbreak solution available. Tethered means that each time you reboot your device, you will need to plug it into your PC or Mac in order to boot it into its jailbroken state.
Steps to Upgrade iOS 5 on iPhone 4 While Preserving Old Baseband:
- First you will to need download the latest version of TinyUmbrella here that supports the iOS 5.0b1.
- Start TSS Server
- Restore iOS 5 stock IPSW. Download here if you have a developers account, if not, you can easily download them off torrent sites by searching Download iOS 5 IPSW in Google.
- You will get error -1
- You will get stuck in recovery mode.
- Now jailbreak using Redsn0w using by following this guide but skip steps 1 and 2.