I administer the Blackberry data portion for my office. We use T-mobile. At our office, if we have someone who wants to use their BlackBerry as a phone, we have them assume responsibility for the phone (with data). We transfer everything over to their name. They receive and pay for the bill. We then have them submit an expense report (about every three months to cut down on the accounting work) to recoup the fees for the data portion.
You may want to speak to your company also, and see if they are willing to let you do this.
There's no I in IT.