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.