For my W3C work, I (and a good chunk of the W3C Team) use Vonage as a Voice over IP service that allows me to participate to teleconferences, call my colleagues, etc. for a very low cost.
But one of my issues with it is that, being with a US number, you can get spammers calling you at US hours, which may or may not match the actual timezone you’re in. I had asked a while back to the technical support in Vonage if there was a way to ask your line to be off (i.e. directly on voicemail) at well-defined times of the day, but to no avail.
Instead, I adapted a script written by one of my colleagues (Ted) to use their Web interface through scripting, primarily based on curl.
Now, with this script, I call set my line on and off with a simple call à la enable-voicemail-vonage on or off; which also means that I can call the said script from a cron job if I want it to be set on and off at a given time in the day…
Of course, I would feel more confident in the reliability of the said script if I could have used some well-defined HTTP interface (e.g. with a WSDL definition); but for the time being, screen scraping will do.