http://www.asterisk-pbx.hk/2011/11/simple-ivr-and-queue-example-where.html

A simple IVR and Queue example where customer listens to marketing materials and also can leave voice message by '*'

http://www.digium.com/en/products/switchvox/support/a-basic-ivr

http://blog.eduguru.in/asterisk-creating-a-simple-ivr-menu/