- Do not keep notes re customer calls and/or share them with co-workers.
That way, customers will have to re-explain their problem to every person they talk to.
- Speak with a thick/foreign accent.
- Play obnoxious music (preferably a song with a incessantly-repeated lyric that can't quite be understood).
- Use an audio system that sounds like a 30-year old sun-baked drive-in speaker that's been stabbed with a knife.
- Interrupt the music every minute or so with a recording stating how incredibly important the customer's call is.
This repeated interruption repeatedly makes the customer think that a person is picking up.
This breaks their train of thought, and helps prevent them from doing anything useful.