If you're paying $29.99 for your Blackberry Email & Web plan then the tethering would be an additional $30. Since they're each a seperate price the usage and allowance are also seperate. Your $29.99 data plan for the device is truly unlimited, there is no cap for data usage directly on the device. Tethering is where you're limited to 5GB/month but the usage is only for tethering. Any data usage you do directly on your device will not count against your 5GB for tethering.
In your MyVerizon account it will break down the usage for you between your normal data and your tethering so you can keep good track of it.
I have the same plan as KayinFl...nationwide select family 700 and two of us have a $29.99 data plan for our blackberries. I know this has been answered before but I wasn't clear on whether we had to pay an additional $30 to tether?