We've got our phone set on 2 rings and then the ansa phone kicks in. If it's a legit' call then we pick up as soon as we recognise the voice. If not we leave it, or more usually the caller rings off without leaving a message. Get number withheld block, that cuts 90% of the sales calls out straight away. We've got just about a 100% success rate on binning sales and other calls.
Damn trying to find that funny video (only sound) where the bloke in US gets a call and tapes it while pretending to be a cop investigating a murder. It was like a radio show they were playing it on. Bum where is it now.