To send an SMS message using the Vonage PHP SDK, you will need a Vonage API account and your API Key and API Secret. You can create a new PHP script or use a web application framework like Slim to send an SMS with as few lines of code as possible. With a raw script, you can send a text message by requiring the Vonage PHP SDK and creating a Client object with your credentials and message data. Alternatively, you can plug this into a basic web framework like Slim to POST a JSON body containing the text to be sent, making it easier to integrate with other applications.