Our exchange servers were recently replaced from 2k to 2k3 with out issue. Since rolling out office 2003 when checking VM it states that new email messages are new messages as well as saved messages, this did not happen previously. Unity 4.0(3)sr1.
If you are not using UM, then you should not be sending vm to the same account that gets emails; that is the UM.
Unity in VM-only mode is not supported with exchange 2003.