Roaming?

Talk about a bummer! I have had Sprint for YEARS and today when I logged on to Sprint online I saw an alert about almost going over my Data Roaming. I have NEVER seen this before so I called Sprint CS. I was using a Palm Pre for the past year and used the Hell out of my data and not once got billed. CS told me that the Evo does carry a 3GB cap on data roaming and that I must have been roaming while surfing the net. WTF? I am tempted to return this phone if it is going to cause this headache. They advised me to turn off my PLR settings so I don't go over my limit. When I asked them what I was paying the extra 10.00 for they said it was because the phone has HD.
ARG! I love this phone but what's the point if they are going to nickle and dime me?
I still have no idea when I could have possibly been roaming unless I was in an elevator or something. Does anyone have any ideas? I am open to anything to help me keep my EVO. I live in an area that is supposed to get great 4g coverage but NOT. It jumps between 3g and 4g...mostly stays in 3g.