[Asterisk-Users] Swap between callers

[Angus Comber]

Hello

On business phones it is often possible to have call waiting (think that is 
the feature) whereby if you are talking to a caller you can see another 
caller has called and you can swap between callers.  For example, to say 
hello, I am on call with someone else now can I call you back.

How can this be implemented using SIP IP phones.  Do you need to setup two 
or more lines?  How is it done?

Angus