The plan is called PhoneFirst Web. It is not the same as T-Zones.
T-mob doesn't require the Web for Smartphone plan for an "unsupported phone". Those are the words you need to use to describe your N900.

I still think the easiest thing may be to just tell them I'm using my old N75, which DOES have 3G support. But many good suggestions have come up, so thanks all!

mine is t-mobile smartphonw unlimited web

worked for me!

for voice plans.

data only is $39.99

to OP: as others said, do it online, choose any featurephone - mission accomplished

to others - i selected the nokia 6600 as my device online some time ago and it is stll shown as that, so I don't know about it being recognized as an n900, I'm in the US, btw.

i suspect that, if you go really heavy on data, an audit is triggered.

dunno, but I've been getting 3.5G access since June for $9.99 with no adverse effects - besides hi batt drain.

I guess the problem is they are sending me a Cliq XT. It was free, so i figured why not, send me the phone and I'll just Ebay it and get some money for it. Not even going to use it at all. So they think I'm using an Android phone now, which requires the 29.99 Data Plan. So I have to call them or go on line and put in the serial of another phone, like I said my old N75, and go to the lower data plan. So unfortunatly I have to convince them I'm NOT using the Cliq they are sending me.

if you get it free like that, you are probably under contract with the 29.99 plan. so you can't change

Gorilla, if you got a free phone, there IS a contract, thus contracted feature. You have 3 options to remove that required feature:

1) Return the Cliq
2) Keep the cliq, but buy some cheap phone from an official store (online, t-mobile store -- but not walmart, radio shack, etc). May have to wait 30 days before they let you do this. New phone, new contract, new contract tems (eg, no required web)
3) replace required web with required unlimited messaging - if you are on a family plan, then you will have to remove family messagign for this to work.

Option 3 is probably the easiest, though.

Well, I wanted to sell the phone to make a few bucks, since i got it for free. But I have not even received it yet, so very easy to take the unopened box to a T-Mobile store and just say, give me that cheap crappy texting phone instead, and switch me to the cheap internet as well. Then go home and pop the sim in my N900? Right, Hu Hu? High Fives? Anyone?

But then I would need to do some 'tweakin' as I have seen in this board, in order to get the internet to work correctly on the N900, right?

Potential contractual violation aside, I'd be more inclined to say that T-Mobile is being a jerk by charging two prices for the same thing, than to blame you for doing something about it.

...I'm fairly certain the developer was entirely mortal, but... point taken. XP I tend to just set it up manually, however.

The "no tethering" bit assumes they can enforce it, which assumes that they "own" your phone as per usual. The N900, of course, is your own darn phone, and they can't do a thing about it. That's the way it should be.