Automate phone system backend (simple)

Looking for some expertise and a bid on a project. Requirements: - User can call a phone number, enter a code, and hear a pre-recorded message (mp3 / wav?) - Potentially other menu options and re-directs in the system. - Interaction with the user can be touchtone key-punch (does not need to be voice command) We would provide the server and set up -- but are looking for advice on setting up a server for cheap that can do this. I believe they are IBX servers or something? Also, we would not need front end web development for this part of the project. We'll be able to do that ourselves - or potentially hire someone on here for it. But - this bid should only relate to the phone system portion.