Can someone please explain exactly what the difference between AT&T's BlackBerry Personal and BlackBerry Enterprise plans are?

I had a chat with an AT&T rep online, and upon asking him if any of their 3 personal plans (BlackBerry® Personal, BlackBerry® Personal Bundle, and BlackBerry® Personal with tethering) supported the use of a BlackBerry Enterprise Server, he told me that all 3 of them should. However, I keep seeing everywhere that you have to have a data plan provisioned for BES... what exactly is the difference?

BES allows you bb to communicate directly with your company's email server giving it access to your emails (of course) your work calandar, tasks and notes.

With BES, all of these things wirelessly syncronize with the server and allows you all of the contacts on the server.

With BIS, you get access to your pop email accounts (gmail, yahoo, hotmail, etc) on your bb and allows you internet capabilities.

Bascially, BES is for a corporate server and BIS is for personal use.

If you have a BIS only data plan, the device cannot be set up on a BES. That is, there is no option for 'Enterprise Activation', which is used for BES setup.