You are trying to develop an IVR (Interactive Voice Response) system. For asterisk it is do-able by using PHP-AGI with its ability for:
- presenting voice response (recorded speech or text to speech)
- getting the tone pressed
- ordering command for asterisk to: dial, transfer, pickup, hangup, etc
- integrating with another resources such as web service, database, etc
- integrating with payment gateway such as credit card, paypal, etc
- etc
Let me know the detail of your project.