You already have an unlimited data plan which is the $29.99 a month.You are covered 
TheGreatOne is correct, you have unlimited data, no worries. Also check out Slacker Radio, and tv.com apps 
The reason Pandora puts that in is you have to remembr that although every Android carrying cell company *currently* requires unlimited data plans for their devices, that doesn't mean it wil hold true in the future, With the warning there, they don't have to keep track of who does and who does not require unlimited data plans. Also, I sure that on a GSM provider like T-Mobile, it's possible in the correct circumstances to put a SIm card from a plan without unlimited data into an Android phone and somehow get charged some outrageous data charges in te process, especially if a user were to circumvent any safe-guards T-Mo or AT&T have put in place by rooting their phone. You also have to consider someone who roams in annother countery, such as Canada where your "unlimited roaming" wouldn't apply.
Add to that the fact that Slacker is available on other platforms other than android, possibly on a phone that might not require an unlimited data plan, and it just makes sense that they use a "standard disclaimer" when the apps installs. Not that they should be required to warn a user, or could be held liable if someone used a huge amount of data and racked up a multi-thousand dollar data bill, but they at least are trying to make a user aware of the fact that the app is going to be using serious amounts of data.
