Chris says Voicemail for iPhone will allow you to check your voicemail messages on your house or business line from your iPhone.
"You can think of it as "Visual Voicemail", but for your Asterisk PBX numbers instead of your AT&T cell number," he writes. "The technology behind it is Asterisk (The Open-Source PBX), with iUI, Joe Hewitt's UI interface for iPhone. This software can be installed on any Asterisk server (though you will want to use one that is available via the Internet) and will allow you to check messages, listen to messages, delete messages, move messages, and change voicemail settings - all from your iPhone."
If you are looking for a download link, there isn't one yet. Chris says that after he cleans up portions of the code, he'll release the software under GPL or some other free public license.