Problem being, that's a function of the phone. Asterisk can only send the call to it.
Asterisk can't determine where the sound comes out of the phone or whether the phone should auto-answer after X seconds/rings.
Vicidial can send a popup, and Firefox can play a sound as a result of the popup. Or Vicidial could even "Play some background music" (which could sound like a train horn if you like). But it can't affect the phone in any way other than sending a call to it.
So ... if you wanna get weird, a second call could be generated to another line of the phone, ring once and hang up ... then ring the real line which would be set to auto-answer?
Some phones have the ability to accept html strings for display on the LCD, but I do not know if that allows for any form of sound generation on the phones (and I'm pretty sure that would be very limited to specific phones).
Happy hunting?