It IS confusing! and your right! From the best I can tell, its not available to Treo owners. At least if it is, I can't find out how a Treo owner would activate it. Reading their web site on the CV (cingular video) all you do is activate the service and click on the CV icon in the interface. That reveals all the content currently available. Pretty hard to get to work if you don't have that icon . . .
But as far as losing a grandfathered plan, its actually cheaper than the current "unlimited MediaNet" package. Unlimited MediaNet was just that, for $20 per month. This new max plan offers unlimited data, 200 text/MMS messages and CV for $20 per month! They also offer a further (to further confuse you) max plan that includes more text messages for $30 per month.
Of course you still fall into the medianet for non-pdas vs PDA connect for PDA's and how cingular breaks its own rules to accomodate its customers, ripping off some, while gladly accomadating others . . . And when its new high speed data becomes available, I only see it getting more confusing . . . .