PHP Android Text Message Manager

We require a PHP script and an Android application, which allows users to send text messages using their phone by entering the required information into a web form on any device with Internet access or passing them as POST or GET requests (using a unique API key for identifying the user rather than username + password), as well as to see incoming messages online or exporting them as an XML or JSON file. Users will authenticate with user name and password. This combination will be necessary to access the web forms as well as for the Android application to authenticate to the server. It will be possible to send the same text message to multiple recipients at the same time. There will also be a feature to schedule the message to be sent at a specified date/time. Scheduled messages can be deleted or changed at any time before they are sent. All messages will be stored in a MySQL database. The Android app will have settings to control how often the server will be queried for new messages as well as to change the server. You can not use GCM for this project. While we would prefer having a solution which does not require any server applications beyond a LAMP web server, if you require any server application, you can either develop it yourself, or use open source alternatives (such as RabbitMQ).