Convert site from ASP & Asterisk to PHP / Twilio

Project Detail: We have a website/application that is a service which provides a user the ability to purchase calls, record messages, upload mp3 files, and schedule those calls to go out. The site has been completed with ASP.NET and Asterisk. We need this to be moved over to PHP and utilize Twilio (or a close alternative) as the IVR / Call application. The front end design has been completed (Using Bootstrap). Your code will need to be able to provide the functions for a user to place orders, record their calls, schedule a time for their calls to be placed, and as well as handle billing with a service such as Paypal or Stripe. The Paypal coding has been completed and is included in the ASP code that will be provided. The back end needs to have the ability to manage customers, users, files, artists, etc. This current interface was completed, but is in ASP.NET. Complete files will be provided. Database: The DB is MySQL and a complete .sql dump file is read to easily recreate the existing structure. Functions: Since this is a site/application that allows you to schedule phone calls/ messages / greetings there must be a routine/job that checks the call queue and send the calls at their pre-determined times. The time setting must be based upon a selection by the user (ie: CST, EST, etc). If a call fails, it must be reported and remain in the queue until the call is completed or until it is determined that it is not possible to complete. In addition to being able to record a greeting, the user will select a song to go along with that greeting. The user should also be able to upload their own mp3 file for playback during the call. Uploaded MP3's must be deleted from the file system after 3 attempts. File storage should be via AWS or an alternative cloud based infrastructure such as Google Cloud Storage or Azure. In addition to the single users of the service, there are partners who will receive preset codes to sell to their customers. That customer should then be able to call into our toll free line, enter his/her pre-assigned codes and record their greeting. Partners receive a preset batch of codes. There must be a process in place to sufficiently randomize and secure the codes to ensure a simple guess will not be able to activate a card/code. Keep in mind the numeric limitation since 100% of the process could happen via phone. In addition to messages where a user receives a call from our service at a scheduled time, there must be an ability for a user to call in to retrieve a message with a code. A complete spec, walk-through, and screenshots, are available upon your indication of interest.