[tsac]

first the Blackberry must be unlocked to use it on another carriers network so first question is what carrier is it associated with? Also it sound like it's asking for enterprise activation. You wont need a BES account unless your intending to run it as a cell from a company and have need to manage the cell phones.
Normally a 9800 is connected to a BIS type account from a carrier and that requires a specific blackberry data plan. with that plan you can activate email on the phone and use it for data and other uses..

I would call your carrier and discuss options.

Unlocking the phone if locked to another carrier is possible but may need to be done only if the phone is not originally a Virgin phone.
You said it is open to any network so call virgin and set up a blackberry plan.