Treonauts published a review of the Cardo Scala 500 Bluetooth Headset which is considered a worthy alternative to the Palm Bluetooth Headset for the Treo 650. There are a couple of things that make the Cardo Scala 500 stand out and probably make it a better choice:

• there's a great deal on it at Amazon.com right now,
• it has better battery life than Palm's own model,
• it comes with clips for your glasses, a belt clip holster, and a neckband.

The chief drawback seems to be that the Cardo Scala 500 is not USB-chargeable, but they make up for that with a very compact charger. I charge my Treo by plugging into a power strip anyway, so I'd need a second outlet which I can easily find.

The current price on the Cardo Scala 500 is just about two times the list price of a replacement Treo 650 wired headset from Palm. If you need a new headset now (I know I do), maybe it's time to consider going wireless.