Check these out:
http://www.slonet.org/~rloomis/mailcall.html
http://emailsounds.phatster.com/
http://www.eventsounds.com/wav/idmail.wav
Edit: Most of wav-files wont work whit 7650 so you have to covert those to "8-bit, mono, unsigned". You can do this whit a GoldWave for example...