Since I didn't find it in search, I thought I'd post about getting the iPad data plan on my N900. (For those who don't know, the plan is currently $15/mo for 250MB or $25/mo for 2GB with no contract).

Step 1: I went to the local AT&T store and asked for an iPad SIM card. For $15, I was sold a normal sized SIM card with perforations to turn it into a MicroSIM. I recorded the ICCID number and put the card in my N900.

Step 2: I followed the instructions from http://forums.macrumors.com/showthread.php?t=928196 to activate the SIM. Basically, go to https://dcp2.att.com/OEPClient/openPage?IMEI=X&ICCID=Y (filling in your phone's IMEI and the SIM's ICCID) with a browser setup to send an iPad User-Agent. I used Safari since the page contains some non-standard CSS.

Step 3: On your N900, go to the "Connections" list inside the "Internet Connections" section of the "Settings" app and tell the "AT&T Internet" connection to use "broadband" as the APN. I also filled in the username and password I had set up in Step 2.

After waiting a bit (I don't remember how long), I had internet access via the iPad data plan.

For the Canadian customers, Rogers is offering 30$ for 5gb for the iPad data plan, and you don't need a special sim, just call them up and switch plans

If you have T-mobile coverage, then 10$ web plan, 24.99 unlimited or 30.00 unlimited are more attractive than AT&T cap. (Eventhough its unlikely you will hit 2GB). but I like the word "unlimited".

Presumably you would be breaking some Ts & Cs by doing this?

I have AT&T and you got the typical data plan they are giving every one iPAD and the full line of smartphones there will not be a problem with the T&C's.

I have had a "Unlimited" data plan with AT&T for several years so I grandfathered and kept it when they started selling the $15 & $25 deals back around July.

But you're on 2.5G/EDGE?