For AT&T Custom Primary ISDN protocol, the "L" flags only apply to the NT DMS10/DMS100/DMS200/DMS250 & DMS500 switches. The WECO/LUCENT/AVAYA 5ESS switch does not have trunk group flags.
Be careful about what some of these "provides" call ISDN protocol. Knowing what CO switch is being used is very important. The Avaya Merlin Legend/Magix System Planning document is very handy for knowing what is needed for PRI ISDN service, etc.
....JIM....