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See here
Corporate BES IT Policies
IT policies can be extremely tight, not allowing users to visit certain web domains, access types of domains such as streaming audio/video, not allowing Instant Messaging, etc. IT Policies can also restrict users’ abilities to add software to a company-owned handheld.
Be aware that if you wish to use your personal device on a corporate BES, you must obtain permission from the Admin.
You must also be aware that if you do add your personal device to a corporate BES any existing IT Policy will be installed onto your personal device taking control out of your hands.
Note that anything done on a BlackBerry handheld connected to a BES system can be seen by the BES Administrator. That includes personal email, IMs (if even permitted by the IT Policy), websites visited, etc. You should remember that with a BES-connected BlackBerry, there is nothing private.
If this bothers you then do not place your private device on a company BES. If you need to have personal information kept personal then purchase your own BlackBerry and carry two, yours and the company’s.
Also keep in mind that many companies have policies that if an employee attempts to bypass the corporate IT Policy, that employee could be subject to discipline up to and including possible termination. Do not look for ways around a corporate IT policy. Get your own device and use it for your personal stuff. Unless, of course, you are looking for a career change.