This tutorial describes how to use the popular cURL commandline tool to upload a voicemail greeting using the Switchvox Extend API.
I wrote a very similar tutorial a while back called Interacting with the Extend API using Wget. cURL is very similar to Wget, but is a little better at uploading files, which is why I choose to use it for this tutorial. cURL can be found on most Linux systems, and can also be downloaded for all major operating systems. For more information on cURL, see Wikipedia.