I am a long time AT&T customer and had the iPhone from the beginning. I have unlimited data grandfathered in from the beginning. I am hearing that if I upgrade from my 4s I will lose this. Any idea if this true?

It is true. I think the only way around it is to pay full price for the phone - no upgrade discount. This was the case in November; don't know if that's still in effect.
I am a long time AT&T customer and had the iPhone from the beginning. I have unlimited data grandfathered in from the beginning. I am hearing that if I upgrade from my 4s I will lose this. Any idea if this true?