From IGNCube:

The company clarifies which "new" Sonic title is GCN bound.

July 02, 2002 - Yesterday Sega announced that it would deliver GameCube owners two new Sonic branded titles. The first, Sonic Mega Collection, would appear to be a compilation of classic Sonic games. The other, originally called a new Sonic Adventure title by Sega, is in fact not the case at all, according to the firm.

Sega clarified earlier today that its US and Japanese branches had a "miscommunication" yesterday and that the previously announced upcoming Sonic Adventure title is really a port of Sonic Adventure 1 to GameCube.

Sonic Adventure 1 first appeared on Sega's ill-fated Dreamcast console in September of 1999, already making the offering nearly three years out of date. The title, which neatly situated Sonic the Hedgehog into smooth-rolling 3D environments and injected lots of speed into the fairly straightforward play mechanics, earned a modest 8.6 rating by our notoriously overzealous sister site IGN Dreamcast.

When asked what changes would be made to the title for its GameCube debut, Sega said that it could not offer specifics at this point in time.

More as it develops.

Source: IGNCube