Pick-up any line at any time...

I just purchased 5 of the 25403 GE-RCA Phones, and I tried getting customer service on the following issue:
When anyone is on any line, you can just pick it up and listen in, is this normal?

I just put down the phone with your customer service, and I must say: 1) or the person on the phone has no idea how this thing works 2) or this product is outdated and sucks.
Explain to me if EVER saw a phone (never mind a business phone) that you can just pickup any line that is IN USE? I used older models and lower brands before, never in my life have I heard such a thing!
The guy tells me that there's a Privacy button on the phone that I can use, well thanks, this Privacy thing is just like any other DND (Do Not Disturb) button on any other phone out there, you cannot receive any other calls while you're in that mode, and you have to set this button every time you make a phone call and you don't want anyone to be able to pickup or listen in, is this for REAL???
Anybody out there that DOES know anything about this, or is there any help available to return these phones???