Analogue 5.8GHz phones are easy enough to listen to, however high enough frequency to be out of reach of the cheap scanners without a block downconverter. The only cordless phones that are relatively secure are those that are digital as previously mentioned. Also, it's worth mentioning that many cheap 5.8GHz phones only transmit 5.8GHz one way and use a lower band (heard by more scanners) the other direction.