I have a BES Blackberry with AT&T.
If I purchase an unlocked Blackberry for personal use and use it with the BES AT&T SIM card occasionally, would it work?
I think you would have to "change devices" each time as only one can be active on your sim card at any time. I could be wrong - but that has been my experience with T-Mobile.
Just a note of caution here. If you have a company supplied BB, I would not try to circumvent their rules and policies and try to put the SIM in your personal device. That is, if you value your job. The best solution is to get your own device and pay for it.