The following is a step by step guide to factory reset the HTC Inspire 4G from AT&T. It will wipe out all data and applications on the phone.
1) Choose Settings -> Privacy -> Factory data reset -> Reset phone
2) Confirm with Erase everything
1) Hold the volume down button while power on or restart the phone
2) You will not get to the hboot menu and choose "Factory Reset". You may navigate the menu with volume up/down button and select with power button.
3) Now the phone will wipe out everything and reboot itself. The phone will be factory reset after the process is complete