While most VoIP devices are made for Skype, IPEVO has made a version of its TR-10 conference phone with the Mac in mind: It can be used with both iChat and GarageBand.
For iChat conversations, the device can be used either as a speakerphone or traditional handset with full-duplex audio and echo cancellation. The buttons on the front of the device can be programmed to start iChat or record calls.
For GarageBand, the TR-10 can be used as an audio input device to record podcasts. The device only works with a Mac.
IPEVO sells the TR-10 for $79.90 in its online store.