At&t Data Plan Concerns?

I purchased a Blackberry Torch from AT&T a few days ago replacing my Samsung Impression (which was not a smartphone). I was concerned when the at&t rep who helped me at the store said that they no longer have unlimited data plans and I went with the 2gb. However, after doing some research I have found various people mentioning that if you were a customer who had unlimited data service before they changed their plan that you could keep that the same and use it with your new phone. I DID have unlimited data on my Samsung Impression and obviously had no worries about using data and surfing the web. The at&t rep never mentioned that I could keep my existing unlimited data plan. Would I only be allowed to do so if my previous phone was also a smartphone? Doesn't quite make sense to me. Any information you all have would be greatly appreciated. Thanks in advance.