Apple's device tracking, locking, and wiping tool Find My iPhone is available for free with the iOS 4.2. By default it only works on the iPhone 4, f ...

It's easy to log into iCloud on your iPhone to access and manage your iCloud account. To log into iCloud on your iPhone, you'll have to sign in with your Apple ID through the Settings app.

I then entered DFU mode and restored my iPhone 3GS with this iOS 4 firmware. At first I also applied my previous backup and then couldn't get a wireless signal through T-Mobile.