I think you want Prefix mark. You set this in the route: Below is from the DOC's
For a WATS trunk, the Prefix Mark is the same as the local CO trunk.
Service/Feature
Enter up to 15 characters to identify the Service/Feature carried by the
information element (IE) in a call in this route pattern. This field is required by
Call-by-Call Service Selection, and Network Call Redirection and Transfer.
Service/Feature appears when ISDN-PRI or ISDN-BRI Trunks is y on the
System-Parameters Customer-Options screen.
Valid
entries Usage
0 ? Suppress a user-dialed prefix digit 1 for 10-digit FNPA calls.
? Leave a user-dialed prefix digit 1 for 7-digit HNPA calls.
? Leave a prefix digit 1 on 10-digit calls that are not FNPA or
HNPA calls.
Do not use Prefix Mark 0 in those areas where all long-distance calls
must be dialed as 1+10 digits. Check with your local network
provider.
1 ? Send a 1 on 10-digit calls, but not on 7-digit calls.
Use Prefix Mark 1 for HNPA calls that require a 1 to indicate
long-distance calls.
2 ? Send a 1 on all 10-digit and 7-digit long-distance calls.
Prefix Mark 2 refers to a Toll Table to define long distance codes.
3 ? Send a 1 on all long-distance calls and keep or insert the NPA
(area code) so that all long distance calls are 10-digit calls. The
NPA is inserted when a user dials a Prefix digit 1 plus 7-digits.
Prefix Mark 3 refers to a Toll Table to define long distance codes.
4 ? Always suppress a user-dialed Prefix digit 1.
Use Prefix Mark 4, for example, when ISDN calls route to a media
server or a switch that rejects calls with a prefix digit 1.
blank For tie trunks, leave this field blank.
1a2 to ip I seen it all