I have put a butt set on the line coming in to the the dsu II and everything works fine.

Which means your hear good DTMF of all digits at least 1/2 second long right?

The voice mail system is the from the phone company.
So it's a service provided by the Telco, like here we call it "Answer Call"?

it has nothing to do with the dsu II
no one has any trouble unless they dial through the dsu II and use a seven.

Ok so give me the senario, what are you using the seven for? Retrieving a message? Going to a mailbox? You are describing this as though you think the problem is with the DSU if you hear good DTMF through the DSU and it is an adequet length, it ain't your dsu, it's something at the other end or in bettween, like maybe a repeater on the Telco side.

Reliable Telephone Service