AT&T MERLIN LEGEND System Reference Manual page 268

Features
Feature Interactions
Callback,
Camp-On,
Park, and
Transfix
Pools
Queued Call Console
System Access
Related Features
Returning Callback, Camp-On, Park, and Transfer calls cancel Line Request.
Line Request cannot be used for a Pool button or for a busy pool in the
Hybrid/PBX mode.
Line Request cannot be used on a QCC.
Line Request cannot be used for an Intercom or System Access button.
Callback
Line Request 2-219