Sonic Spinball has been released on RealOne arcade. You can download it for free (for one hour), and the full version costs $14.99. Sonic 3D (most likely the Genesis version) will also be released in May 2003, according to Sega’s RealOne page.
It seems that the option to lock onto Sonic 2 and 3 was not present in the RealOne version of Sonic & Knuckles, as this information was just copied off the box sleeve onto the information page, and not actually present in the game.
The palmtop Sega games, including Mean Bean Machine and the 8-bit Sonic the Hedgehog, will now be available for download on Zire 71 and Tungsten C palmtops, in addition to the Tungsten T.
Source: Sega.com