On analog lines, you are lucky to get caller ID, that is the number being where the call is originating.
No “called number” on analog circuits.
If you have a Quintum, there is field called “access number” ,on the PSTN trunk group.
If your billing system could handle that number and change the rate based on that number, you could create two diferent PSTN groups, with diferent “access numbers”. Direct the calls from the 1800 number to one of the groups, the local calls to the other group.
Not very eficient use of your trunks.
It will be better to get a digital gateway and a PRI from PSTN.