I've been a Verizon Wireless subscriber for about 10 years now. I signed up for what was called their "450 minutes + unlimted web & email" plan many moons ago.
After upgrading my phone to a shiny new Samsung Galaxy Nexus (SGN), I started watching old episodes of "Heroes" while slogging out my cardio workouts at the gym. About a week later, a data usage warning indicator appeared in the notification area of the phone. I opened up the data usage stats to see that I'd already consumed over 1GB of mobile network data traffic. Actually, 1.59GB between Dec 27th and Jan 3rd:
Just to be sure this wasn't going to get me into trouble, I sent an email to Verizon Wireless support and in reply I got the following voice mail. The short version: My grandfathered account is in fact as unlimited as unlimited can be. No cap, no additional charges.