If it's only web and media messages, sounds like you don't have 3G... either that radio got turned off, or your carrier shut off your account. I'd say you accidentally toggled off 3G. You can get it back under Settings > Wireless & Networks > mobile networks (enable) (I don't remember if this is correct for Android 2.2, which I assume you're running).
Or you might have a 3G toggle widget on your homescreen...