It is no longer necessary to physically attach a tap on a wire to listen in on cordless phones, or, in the instance of cell phones, there is no wire at all. There is a very weak radio signal that is supposed to be scrambled, then deciphered by the receiving instrument, but any technology that can scramble a signal is capable of reading and deciphering it, even if it is not the designated recipient.
It has never been illegal, in the strict sense, to listen in on radio transmissions, as it would be impossible to enforce the prevention of tuning into any frequency on the scale. Either all frequencies would have to be prohibited, or none could.
About 25 years ago, it was possible to tune into the conversations on a cordless phone on a UHF TV set, somewhere in the upper end of the range. Didn’t always know who the persons speaking were, but by a very slight retuning of the dial, several different conversations could be picked up.
Perhaps the technology has grown more sophisticated since then, but so has the capability to pick out a particular line of conversation.
That is incorrect.
The Electronic Communications Privacy Act made it illegal to listen to cell phone conversations, and also made it illegal to sell radios (scanners) that could receive a particular band of frequencies that where used by cellphones at the time of the laws passing (the 80s or early 90s I think) .