If you have downloaded iOS 5 beta, you must first activate your idevice to run it. Activating firmware means is that you have to get the UDID of your device and get it registered with the iPhone Developer Program before you can start (legally) loading beta firmware on it and you don’t face any problems while synchronizing with iTunes. Installing beta firmware on unactivated device will make it useless. Here is how you can activate iOS 5 beta 1.
Bypass the activation process and run iOS 5 firmware. This hack will not work on the iPad 2. On iDevices with a cellular modem, this may permanently upgrade your baseband, and will also prevent activation with your carrier as you are bypassing it. This method is not a jailbreak, but after using it you can use iOS 5 beta without activating it. This iOS 5 hack exploits a security flaw in the activation screen. Requires no hacking or jalbreaking and is super easy. Here it is: