I just picked up one of these little toys on eBay for under $100. I had to put new firmware on it, I guess OfficeDepot was selling them and didn't want you to re-provisioning them. They no longer have them in the store or online. I got the latest firmware (WV.00.03 - Dated Jan 2006) and new manual off the Zyxel site. Go to http://www.us.zyxel.com/support/download.php and select VoIP and Prestige 2000W V2.
Now it all works great. Have made a few dozen calls and received as many on it. The wireless works great all over our office and at home too. Nothing special in any of the configurations. I love my new toy. (Oh wait, work paid for it, it's a tool to make me more productive.)
If you have one with old firmware, get the new firmware and give it a try.