runlun, are you sure it is dialtone timeout that is the problem?
More likely it is the interdigit timer for NARS calls to the outside. That is the NIT prompt under NETDATA in the CDB.
I think the max is 8 seconds which, I agree, can be a bit short.
My suggestion is that users pre-dial the phone number before lifting the handset or selecting a line. Then they can dial at their leisure and correct errors before they dial without starting over.
If it really is the dialtone timeout they have a problem with then that is the DIND setting in the TIM_DATA of CDB.