Yes, 3 upgrades to 4. It may (but don't quote me!) even be cheaper to buy 3 first and then upgrade to 4. That happened to me a few versions back with another SoFo product. Existing SoFo users usually get a pretty good deal on upgrades. But they haven't announced the upgrade cost yet.

Check out this page for more info: http://www.sonicfoundry.com/support/ShowFAQ.asp?FAQ=59#1279