Well, WOTC had one under development, and indeed the PHB1 contains advertisements for it (with the groanworthy pun to add anohter PC to your game, as in a Personal Computer).

Unfortunately, the development was a one-man effort and because of personal issues, it was never completed.

To my knowledge, the only VTT that existed at the time was Fantasy Grounds. I have no idea if it supported 4E though.