[cisco-voip] Configuring POTS dial peer so that it returns busy if FXS is in use

[Robert Kulagowski]

I've got an analog fax machine connected to an EVM in a 2851; router is 
running 12.4(15)T4.  If a call comes in on the PRI, the 
destination-pattern is setup so that the call goes to the fax.  However, 
if a second call comes in while the first is still in progress, the 
router is returning unassigned rather than busy.

"max-conn 1" on the dial-peer didn't do what I want.