New phone detected as 4g, bumped data plan, new phone destroyed :-(

Long story short, I have a nokia N95 that will NOT die, best phone I’ve ever owned, but it’s not exactly modern. I am still on my Penn State Staff plan that gets me unlimited everything for a mere 70$ a month (still pretty good I think.)

I got the new HTC Inspire 4G, great phone. Wish I’d gotten one with buttons though. I used my OLD sim card, not the one sent with the new phone when I bought it. When I did the upgrade online, I made sure nothing on my bill was going to change or jeopardize my precious cheap unlimited data plan.

A few days after I got a text from the ATT mothership saying they’d replaced my unlimited $15/mo plan with a 2GB $25/mo plan. I imagine they detected this from the phone’s activiity on the network, but I’m not sure how.

Any ideas as to how they do this? useragent switching seems likely, but also analysis of the IMEI # of the phone might also tell them it’s a 4g?

I ask because my inspire was destroyed (run over by a large truck, whoops!) and now I’m back on the N95. I replaced the cracked screen/digitizer assembly but it seems that the wifi radio and bluetooth radios are both fried and the cell radio is intermittent at best. I’d consider replacing it.