Thanks to Amanda for pointing out this new piece of software from Math Game House Software called iStorm.
The product provides a combination of electronic chalkboard and voice collaboration application for Mac users.
The product costs $19.95 for an individual license and is available for download as a demo (upgradable by a key).
Licensing is available as either a site license or a basic license. The basic license allows two users to collaborate. For site licenses, the pricing starts at 10 users (with a 25% discount) but the license is only for two years.
It also has some cool features for collaboration, such as the built-in calculator that will evaluate simple math expressions and incorporation of TeX compatible scientific formula presenation (cool if you're a scientist or academic).