If you wish to use it for another than SOME COMPANY with voice over IP service, you may need to unlock it first.
Resetting the Cisco ATA to Factory Default Values:
Step 1: Press the function button on the Cisco ATA.
Step 2: Press the digits 322873738 (FACTRESET) then press # on your telephone keypad.
Step 3: Press 3 on your telephone keypad to confirm that you want to reset the Cisco ATA, then hang up the phone.