On my Treo I had an app that could not only block calls from select individuals (or groups) but it could also prevent them from leaving voicemail. It would be great to have something like this on the iPhone as well. It was especially useful for blocking calls and voicemail from work related numbers. Blocking voicemail from these individuals was crucial, otherwise they would expect me to return their call promptly. Sometimes it was the only way I could enjoy a rare day off. The software on the Treo was a little clumsy however. On the calling end, they would hear the sound of the phone picking up and then disconnecting very quickly. Ideally, if there were an iPhone version made, it would be a little cleaner. Perhaps the caller would hear a message that would say something like "This voice mail box is currently offline, please try again later." Just a thought.