Ericsson 250 manual Busy Extension, Camp-on, Press to camp on, Intrusion, Press to intrude

OUTGOING CALLS

BUSY EXTENSION	You call an extension and receive busy tone.
Camp-on	You can notify a busy extension of your call by a muted
	ringing call (if this function is allowed).
	Press to camp on
	Keep the handset off hook. When the called extension
	replaces the handset, it will be called automatically.
	Note: If you receive the busy tone again, the desired extension
	does not allow camp-on.
Intrusion	You can intrude on an ongoing call on a busy extension
	(if this function is allowed).
	Press to intrude
	Intrusion tone is heard and a three-party call is established.
	When the called extension replaces the handset and you keep
	off hook, the called extension will be recalled automatically.
	Note: If you still hear the busy tone, then your extension does not
	have the authority to intrude or the desired extension is protected
	against intrusion.

11	BusinessPhone 250 / BusinessPhone 50
	Standard Telephone / Economyplus Telephone