"Ads" are advertisements. In AmE, we call them "ads." In BrE, they call them "adverts."
You put the phone down in order to disconnect, to hang up. In the old days, phones had cradles with a little button inside the cradle. When you picked the phone up, it released the switch, giving you a "dial tone" and allowing you to place a call. To end the call, you put the phone back down, into the cradle, pressing the switch to disconnect the phone from the call.
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