Extension Roaming allows you to change your default extension to any of the available SIP or IAX channels available on the system. Your default extension is usually the same channel/phone as your mailbox number. This number is displayed in the upper right corner of every page in the end-user panel.
Changing your extension to any other extension than your default extension will cause all calls to be routed to the new phone/channel. Outbound calls from this phone/channel are also modified in such a way that any caller ID's and features will become that of the roaming extension.
Roaming settings are also supported on Aastra, Cisco and Polycom phones. See Phone Browser XML Applications.