By "TOS" = "Terms of Service". Actually they mean to be saying "T&C" as AT&T calls it "Terms and Conditions" (not Terms of Service.)
The Terms and Conditions are here:
http://www.wireless.att.com/cell-phone-service/legal/plan-terms.jsp
People frequently say it "violates the TOS (or T&C)". But go read and search the T&C yourself. I certainly can't find anything that remotely forbids the use of Media Max (or MediaNet unlimited) on a PDA. The T&C explicitly says a a lot about what you can and can't do with different data plans what devices, but nothing remotely close to forbidding Media Max on a PDA.
Why be so specific, but so intentionally leave media max out of the T&C?
I think it's because they don't want to admit that Media Max is a data plan.
It's all fun to debate, but the truth of the matter is AT&T SAYS (verbally) you may not use Media Max on a
PDA, and that's pretty much the end of the argument.
"Media Max" (or Media Net unlimited) is actually the identical data plan to "PDA Max", the iPhone data plan, and the Smartphone connect plan.
They're all the same exact thing 100%. The only difference is the price and the name. So no matter which you have and not matter which phone, they all work the same way.
There is a difference when it comes to tethering and data connect plans, but that's not something you need to worry about. (I'm referring to the addition of isp.cingular access point, which you should never need.)
So can you use it?
If you get Media Max on your PDA, you'll be able to use it and keep it just fine. But when you go to upgrade, you'll be forced to change to the "correct" data plan (a PDA plan.) Or if you do something silly like call AT&T to complain about having data connection problems, the first thing they'll ask is what kind of phone you're using and the gig is up. They won't support you until you switch the 'correct' data plan.
AT&T has recently put in place more strict measures in to the computers system to keep the customer service and sales people from allowing media plans on PDAs. There are ways around this of course. But they've made it so that it's much harder to do accidentally.
I'm not going to say if anyone should or shouldn't circumvent the system to get cheaper data. I just don't care enough to preach either way.
The only reason for a difference of pricing has to do with the history of PDA's being largely marketed toward business people who are more willing to pay a higher price for data. Now that PDAs are much more of a consumer phone, they haven't adjusted the sales practices to be in line with consumer pricing.
It has nothing to do with how or how much data you use. The iPhone is the best example of how they've put PDA data at a consumer price point.
So it (Media Max) does work, and it works identically to the PDA plan if you so chose to do that.