Factory reset locked apple iphone useing the phone 3g?

Got phone at grage sale its locked want to reset it

Throw it in DFU mode (Try this process while pluged in, or unplugged)
MAKE SURE YOU HAVE THE LATEST ITUNES INSTALLED ON YOUR COMPUTER
First turn the phone on
Second hold the power and home button until the iphone Force shuts off
Third, When the Iphone shuts off, Let go of the power button, and keep holding the home button for 15 seconds
Fouth, Plug it in the computer, (If its not plugged in) and it should automatically take you to the restore screen. If not, manually open itunes, and click on the iphone on the side of itunes