Use your written IM policy to establish rules for and set clear limits on employees’ use of IM for personal communication.
Make sure your IM personal usage guidelines are clear and specific. Leave no room for interpretation by individual employees.
Use your employee education program to let employees know that you are restricting personal IM use for the protection of the individual employee, as well for the protection of the organization.
Be mindful of the fact that once you open the door to a little bit of personal IM use, some employees are likely to kick it wide open.