Iphones, Apple ID, and buisness

Hello

I work for a large Australian Company we recently purchased a large ammount of 4S devices for use as corporate mobile mail devices. We have a problem in that when someone leaves the company if they forget to remove the device from their Apple ID, when we wipe the device is locked to that ID. Is their a legitimate way of dealing with this without speaking to company leaver(sometimes people dont leave of their own will) is their an alternative to using individual apple ID's that is still secure for the end user. We dont want our users feeling like big brother is reading their texts.

Thanks in advance.