This is done using ARS and route patterns. Lets see if this has already been set up for you and you are just not using it. Type "list ars an". You should see several pages of info. Starting with the entry 12 look in the field titled "Route Pat" and you should see a number. That is the route pattern that all calls starting with those particular digits will use to call out. At the end of the list will be another (or maybe the same) route pattern for calls starting with 2 through 9. These are your local calls.
Now type "display route <pattern number>". What trunk group (or groups) do you see there? If all your calls are directed to a route pattern containing your local T1 that is easy to fix. Add a new route pattern containing the long distance T1, in it put the LD trunk group number, an FRL of 0, your local NPA, and maybe a prefix mark of 1 (I say maybe a 1 because some T1s will not work if you do, you will have to test it).
Type "change ars an 12" and start changing the route pattern to the new one you added. Before you do them all, make a test call because it might need some fine tuning.
Some of this may already be done but before I can go any farther, I need to know how your existing route patterns are configured.