AT&T MERLIN LEGEND Release 3.0 Programming Summary Manual page 91

Copy Options for Lines/Trunks
4. If you are copying assignments to a block of lines/trunks and one of the
lines or trunks is in use, you see the message Trunk Busy - Pls wait on
your display. The copying for the rest of the lines/trunks in the block is
delayed until the busy line/trunk becomes idle. If you exit without waiting
for the copying to complete, the copying done up to that point is not
canceled.
Lines and Trunks 5-23