I believe Internet streams (iheartradio is definitely an Internet stream) of MLB games are blocked. You have to have an MLB audio account to access MLB games on the web. It’s also a flash player when on the web, so unless they have an iPhone app, it wouldn’t play on an iPhones browser.
MLB on iPhone/iPod Touch - there’s an app for that... get all post-season games.
MLB also has postseason.tv which is a limited internet streaming video version of the playoffs. It uses static cameras you can pick to watch games.
It kinda sucks, but it’s still cheaper than paying for cable for one month, just for the playoffs.