This wiki page contains instructions for setting up Asterisk to use your Project Gizmo account for both incoming and outgoing calls. It’s a nice little hack and sounds like a perfect way for me to tinker with outbound VoIP using a spare box and a generic card that I picked up on Ebay months ago. BroadVoice‘s Bring Your Own Device plans also sound worthwhile.
I’m extremely impressed with the configurability of Asterisk. You can do just about anything you can imagine with it, including routing incoming calls based on caller ID info, and extremely complex outbound routing. With the right configuration it’s no big deal to use POTS for outgoing local calls and even multiple VoIP accounts if one has cheaper rates in a partiucular area, all matchable by dial string.
It’s definitely overkill for a simple answering machine, but it’s truly powerful platform.