In addition to dialing instructions, the system also included a number of other tones that represented various commands or status. 2600 Hz, the key to early phreaking, was the frequency of the tone sent by the long-distance switch indicating that the user had gone on-hook (hung up the phone). This normally resulted in the remote switch also going on-hook, freeing the trunk for other uses. In order to make free lines easy to find, the 2600 Hz tone was continually played into free trunks. If the tone was sent manually by the local user into the phone line, it would trigger the remote switch to go on-hook, but critically, the "local" switch knew he was still off-hook because that was signaled electrically, not by the tone (which their local switch ignored). The system was now in an inconsistent state, leaving the local user connected to an operational long-distance trunk line. With further experimentation, the "phreaks" learned the rest of the signals needed to dial on the remote switch.