1. Connect it to a PC
2. Put your iPhone in recovery mode
2a: To do this, hold the Sleep and home button until the device turns off, then turns back on again with the Apple logo. Once the Apple logo appears, continue to hold home until it shows the iTunes logo with the USB cable.
3. Download the USBView (now called UVCView) HERE (if running 64 bit, find the 64 bit version, I can't find it).
4. Open UVCView.exe and look for "Apple Recovery (iBoot) USB Driver" in the left window under "My Computer"
5: In the right window, look for "iSerialNumber". Under that, it should say "CPID", a bunch of other things, then "ECID". The ECID should look something like this: 000000CFCA016DF5
6. Copy that, and paste it in the text box at
www.PurpleRa1n.com and press enter
7. Save the file for "a very ra1ny day".
*Edit from Twigster9:
8. To get out of recovery mode, press and hold the sleep and home button for 15 seconds, release sleep button and countinue pressing the home button for 2 seconds. Wait awhile for reboot.