There's a decent interview with Pedro Martinez in today's New York Times.
You can get the whole thing here, but to sum it up: He doesn't consider himself retired, he could sign a contract today and pitch in a month, and he is open to pitching this season. Obviously, the Phillies have no need for him, and probably don't have much of an ability to pay him.
But the Times did ask Martinez an interesting question: If the Yankees, Red Sox and Phillies each offered you a contract, which would you pick?
"I’d probably have to say the Red Sox," Martinez said. "I would like to win a World Series in the National League, so the Phillies are in there, too. But for the time I’m going to be playing, I think Boston is more suitable so that I can retire with the Boston Red Sox and go to the Hall of Fame with the same hat."