Recently I had a bunch of trouble with some SIP trunks (read about it at: LG IPECS SIP Trunk Issue) and needed to edit the Least Cost Routing (or Least Call Cost Routing).

The system is pretty basic, landline calls go out of one CO group, calls to mobiles go to another CO group.
There are a couple of tables that control how LCR works: LCR LDT (PGM 221) and LCR DMT (PGM 222).

LCR LDT – Leading Digit Table – PGM 221
This is where the ‘patterns’ are setup, so that the phone system knows what to do with the call, based on the starting digit(s).
Check out this screenshot for a full view:

These are setup under Index 1,
Then in subindex 0-6 are setup for landlines, 7 is setup for the mobile calls.
For each of the Subindex 0-6, it looks at DMT 01
For the Subindex 07 (Mobile calls), it looks at DMT 02

LCR DMT – Digit Modification Table – PGM 222
[To be honest, I have no idea what is actually happening here, except for the reference to the CO/IP Group].
Index 1 routes via CO/IP Group 1
Index 2 routes via CO/IP Group 2
– Index 2 also has an Alternative DMT Index (3) – This is used when all the lines in CO/IP Group 2 are busy
Index 3
– Routes via CO/IP Group 1.

Check out this screen for a full view:

Seems to work alright.