Using a T-Mobile branded phone to avoid data plan?

I've heard that if you use a GSM phone that isn't At&T branded, you can avoid the necessary data plan on smart phones. I have a T-Mobile Blackberry 8950 that has been unlocked for any GSM, will I avoid tripping off the AT&T smartphone police and their effort to force me to get a data plan?

Cancelled the data plan maybe. If ATT lets you off in good faith. If ATT sells the same model of blackberry they may pick up the IMEI code and know that you are using a blackberry and change your account immediately. Possibly they may not know the phone and you won't get charged. It is hit and miss with a blackberry.

I am using my HTC HD2 right now on ATT. I have been for 8 months. Impression data plan. Running both winmo and nexus one froyo build on it too.

The key is if ATT has the IMEI number of your phone in its database. If it doesn't then the phone is unknown to them.

I know that ATT knows all IMEI codes for the iphone (sold world wide and not just on ATT) and the nexus one. And of course every phone they have branded.  I am believing that blackberries might be known to them also but not sure. Now ATT has the samsung captivate. Which is a version of the galaxy. They might know all codes for the galaxy series. Who actually knows? You can also get ATT compatible 3G (850+1900UMTS) phones from canada (Rogers). I was seriously at one time thinking of getting the milestone (The original Droid) from them.

I guess to be safe. If ATT doesn't sell a version of the phone the IMEI should be unknown to them.

As a winmo phone it is buggy. It is hit or miss whether you will have issues. Mine has been very good to me. Out of the box it is bad. Settings need changed and things need tweaked. Not for the un tech person. The android ports have been getting better each week. They have numerous froyo 2.2 builds. None perfect yet but they are working their a$$ off making it better.

Just to let you know the behold 2 from T-mobile has android 1.5 or 1.6 on it. Possibly there are upgrades from xda-developers. But physically that phone is very limited and outdated for android.

And yes the milestone is expensive. Unlocked phones without plans are and will always be much more expensive.

My version of the HD2 is from Australia. It is the T9193. Check the prices on that baby. Used on ebay going over $600. New still about $800. But it is the only HD2 that has the 850 UMTS band to enable 3G on ATT.