Looks like right now your best bet is here
http://www.shop.voipvoice.com/, either the Skype CyberPhone K or the uConnect.
The CyberPhone will let you talk, and change volume, but not do the other functions until they release the Mac driver. The uConnect will also need the Mac driver their developing.
So, why do I recommend a product that has no driver yet? For a couple reasons, their beta testers have reported excellent results with the product, and it sounds like it's close to release. Secondly, I can't find anyone else that's even developing a driver.
I look forward to seeing what other people say on this subject.
[edit] Stupid homonyms...