Despite the long-winded title, this is a very simple application to demonstrate simple receiving of an incoming SMS from Nexmo. When the message arrives, a simple SlimPHP application adds the data to a queue and acknowledges the incoming webhook. A separate worker process then takes each item from the queue, optionally checks the message signature, and writes it to a file.
To get started with Nexmo and for more information about any element of this application, refer to the Nexmo Developer Portal where you will find API reference documentation and code examples in multiple languages.