1. Answer the call calmly and politely, when the schpeel has started, quietly lay the handset on the surface, and go and do something fulfilling. Return to the handset in about half an hour, and they've usually gone.
2. Declare in your first sentence that you are an undischarged bankrupt. That works the fastest.
3. Callers - Learn at least one sentence of an obscure language. When communication can't happen, the caller retreats.