You would normally be on BES if you are running through your company's servers. If you are signed up on your own plan, odds are, and this is not definite, that you are on a BIS plan. You can contact your carrier to verify which you have.
Well if you said that it's on your "company network" which I assume is where you work, then most likely it is on BES. Does the device use company e-mail? If it does, then most likey yes.