You can jailbreak your iPhone 4 running iOS 4.2.1 with greenp0ison (by following this guide) but updating to iOS 4.2.1 can upgrade your baseband that can end making your iPhone 4 unlockable if it’s not factory unlocked. There is a way to update iPhone 4 to iOS 4.2.1 while avoiding the baseband upgrade. To do this, you can follow our guide to update iPhone 4 to iOS 4.2.1 without upgrading the 1.59.00 baseband. A jailbroken iPhone 4 updated to iOS 4.2.1 without updated baseband can be unlocked with Ultrasn0w. Here is the step by step guide to do it:

The jailbreak for iOS 4.2.1 on iPhone 4 is available (check the guide to jailbreak iOS 4.2.1 with GreenP0ison RC 5 here) but updating your iPhone 4 to iOS 4.2.1 upgrades the 1.59.00 baseband that makes your iPhone unlockable (so far) if you rely on unlock.

The following method lets you update to iOS 4.2.1 without updating the baseband and you can use greenp0ison RC5 to jailbreak without loosing the ability to unlock.

Chronic Dev Team has just released the Windows version of greenp0ison RC5 that brings untethered jailbreak for all iOS devices running iOS 4.2.1. Here is the step by step guide to jailbreak with greenp0ison RC5.

Before you go for the guide you must know:

- This jailbreak is for all iOS devices running iOS 4.2.1.

- I will not be responsible for any loss of your device while attempting this jailbreak, do it on your own risk.

- This will not unlock your iPhone. If you rely on factory unlock then don’t update to iOS 4.2.1 as it will also upgrade your baseband that is unlockable (so far).

Update: Follow our guide to update iPhone 4 to iOS 4.2.1 without upgrading the 1.59.00 baseband to upgrade to  iOS 4.2.1 without loosing the ability to unlock.

- If your iOS device is already jailbroken on redsn0w 0.9.x running tethered iOS 4.2.1, you can run greenpois0n again to make it untethered.

Dev-team has released the v1.2 of ultrasn0w that unlocks iOS 4.2.1 on iPhone 3G and iPhone 3GS with baseband 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00. iPhone 4 is not supported as it has different baseband.

Following are the complete guide and details to unlock iOS 4.2.1 on iPhone 3G and 3GS using ultrasn0w.

Important things to know before you go for this unlock:

1. The unlock is for iPhone 3G and iPhone 3GS with baseband 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00.
2. iOS 4.1 on baseband 05.14.02 and iOS 4.2.1 on baseband 05.15.04 are NOT SUPPORTED.
3. YOU CAN UPDATE YOUR BASEBAND to 6.15.00. Read this guide from RedmondPie for full details.
4. If you update to baseband 6.15.00, you won’t be able to downgrade the baseband.
5. It is HIGHLY RECOMMENDED that you should not upgrade your baseband to 6.15.00. Only do this if you are in need of unlock after updating to iOS 4.2.1 or you are suck with baseband 05.14 or 05.15.

The jailbreak for iOS 4.2.1 is now available via Redsn0w 0.9.4b4 by iPhone Dev Team. Here is the full step by step guide and details for jailbreaking iOS devices running iOS 4.2.1

Before you go for the guide, you must know:

- This jailbreak is for iPhone 3G, iPhone 3GS, iPhone 4, iPod Touch 2G, iPod Touch 3G, iPod Touch 4G and iPad running on iOS 4.2.1 only

- Except for iPhone 3G, iPhone 3GS old iBoot and iPod Touch 2G MB model, this jailbreak is tethered. That means every time you reboot your device, you will have to jailbreak it again.

- This will not unlock your iPhone. If your iPhone is not factory unlocked, don’t try this jailbreak because no unlock for iOS 4.2.1 is available yet.
Update 1: Unlock for iPhone 3G and 3GS on iOS 4.2.1 with baseband 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00 is available, click here for complete guide and details. Whereas the unlock for iPhone 4 on iOS 4.2.1 is not available yet so don’t go for this jailbreak if your iPhone 4 relies on software unlock.

- I will not be responsible for any loss of your device while attempting this jailbreak, do it on your own risk

ih8sn0w team has just released sn0wbreeze 2.1 that can jailbreak iPhone 3G, 3GS, 4 iPod Touch 2G, 3G, 4G and iPad and Apple TV.

Here are instructions to jailbreak iOS 4.1 on an iPhone, these instructions are almost same for all iOS devices.

Apple just released iOS 4.2 to developers for all iOS devices. The jailbreak for iOS 4.2 can be made happen using Redsn0w 0.9.6b2. Here is the full step by step guide for jailbreaking iOS devices running iOS 4.2.

Before you go for the guide you must know:

- This jailbreak is for iPhone 3G, iPhone 3GS, iPhone 4, iPod Touch 2G, iPod Touch 3G, iPod Touch 4G and iPad running on iOS 4.2 only

- This will not unlock your iPhone. If your iPhone is not factory unlocked, don’t try this jailbreak because no unlock for iOS 4.2 is available yet.

- I will not be responsible for any loss of your device while attempting this jailbreak, do it on your own risk

Originally, the iPhone 3GS can record 640×480 videos @ 3Mbps. Mike Pan, after having a look at the ARM Cortex processor that the iPhone 3GS uses, discovered that iPhone 3GS can handle 720p encoding because of the capabilities of the processor. He was able to by pass the artificial limit that Apple has placed to enable the HD video recording. This method enables the non-standard resolution of 1080×800 for HD video recording. Mike opted this resolution to maintain the aspect ratio. Here is the sample video quality after enabling HD video recording on an iPhone 3GS.

Here is how to do it:

The Chronic Dev team has just released Greenpois0n Jailbreak for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G on iOS 4.1 and iPad on iOS 3.2.2. Here is how to do it:

Before you go for the guide you must know:

- This jailbreak is iPhone 3GS and iPhone 4,  iPod Touch 3G and 4G running iOS 4.1 and iPad running iOS 3.2.2 only

- I will not be responsible for any loss of your device while attempting this jailbreak, do it on your own risk.

- This will not unlock your iPhone. Upgrading to iOS 4.1 will update your baseband and you won’t be able to unlock your iPhone 4(so far). You can either wait for a tool that can unlock your iPhone 4 after the upgraded baseband or follow this guide to update iPhone 4 to iOS 4.1 without updating the 1.59.00 baseband and then follow this guide to unlock your iPhone 4.

GeoHot recently released a new jailbreak tool called Limera1n. Limera1n can jailbreak iPhone 3GS, iPhone 4 and iPod Touch 3G & 4G. As limera1n requires you to update to iOS 4.1 first, iPhone 4’s baseband also gets updated when you update to iOS 4.1 that makes iPhone 4 unlockable as there is no tool available yet to unlock iPhone 4 running iOS 4.1 with a baseband update. Next release of Pwnage Tool is expected to unlock this.

There is a way to update iPhone 4 to iOS 4.1 while avoiding the baseband update. To do this, you can follow our guide to update iPhone 4 to iOS 4.1 without updating the 1.59.00 baseband. A jailbroken iPhone 4 updated to iOS 4.1 without updated baseband can be unlocked with Ultrasn0w. Here is step by step guide to do it: