Are you sure your E71 is NAM version?? Perhaps you have the EU version of the E71 and you are not aware... Open the battery cover and take the battery out, does it say E71-2 on the silver sticker?? If it does, than it's the NAM version, if it says E71-1 or otherwise, you most likely have the EU version..
Yes, i've checked that out, it's E71-2. i'm pretty sure it's rm-357, as opposed to EU's rm-346 i totally expect my E71(and other US or EU E71) bump into some trouble when it comes to 3G, as you said, compatibility issues about frequency, but I am not a 3G subscriber :)