I think the days of unlimited internet access are coming to an end and all carriers are introducing capped internet plans. The official line from most carriers is that this is due to abuse by small numbers of users who are using gigabytes of data a month through illicit tethering, etc.
Personally, I can understand caps, but do feel that 500mb is a bit on the small size: A cap of 2GB would pretty much cover any legitimate use of a smart phone for a month but would stop people over-using the service to the detriment of others
I wouldn't mind just a flexible cap. As in, say you reach your 500mb limit one month, it would be nice if instead of charging you through the nose they simply increased the cap to 750mb for that particular month for no extra charge.
But of course they won't.