Sony declined to comment on the rumor (same as last time this rumor surfaced), but Engadget reports that it's heading to market "soon" -- like 2011 soon. The prototype unit shown in the blog's photos has a long multitouch enabled touchpad in the center, support for microSD cards, 512MB of RAM, 1GB of ROM, and the screen is 3.7 to 4.1 inches.
Given Sony's push for a fully integrated PlayStation Network across all its devices, a PlayStation Phone doesn't seem outlandish. Getting it to market right after the Windows Phone 7, however, seems risky.
PCWorld.