No, once the messages leave the voice mail system it assumes their being delivered so theres no copy and no way that I know of to change the sample rate. If the IT staff wont budge then the client will have to deal with it unless you go over their heads and plead your case to the higher ups. Theres no real drawbacks to allowing large attachments in. If their worried about the Exchange database size then the users can archive the recorded calls to cd and delete them from their mailbox.