Whisper huskily - "Naughty Nancy here - have you been a naughty boy?"

Tell them you only communicate through Morse code and start pressing buttons

"I told you - I don't have the BODIES"

"JUDY...!!! I thought you were DEAD!!!"

Sing the llama song

Ask if they can smell bacon - and insist that there is a strong smell of bacon coming down the phone

Tell them you left the gas on and will be right back - then simulate an explosion noise down the phone

"No Steve isn't here right now, but great great great aunt Mavis is, shall I put her on?"

Inform them that they need to speak up and see how loud they can get

Other (comment)