Okay, that is fine,
First you will need to record an OGM message, if you go into;
Optional Device > Voice Message > DISA Message , then you will be presented with a list of OGM's, Choose which one you want be sure to label it though! , for example if you choose 507 (OGM/DISA 07).
Once you have chosen your message dial *36 1 507 (or whatever one you chose) and record the message, press dial store to save before putting receiver down.
Once recorded you will then need to create a queuing time table, This is Group > Incoming Call Group > Queuing time table, here make the first sequence your OGM 07 or whichever you chose, then make your next sequence "Overflow".
Next make a hunt group which is is Group > Incoming Call Group > Group Settings , make a dummy hunt group here, call it "IncomingMSG" or something, then go into the tab "Queuing time table" and assign your queuing time table you made.
Next stage go into the tab "Overflow queuing busy" and "Overflow no answer", there input the destination of where you want the calls going after the message.
I hope this makes sense, I know it seems like a lot for such a simple thing.
Thanks