"Multi Ring"?

I’ve been told that Asterisk can be made to ring multiple lines at once IE a user who has a (Asterisk)desk phone and a cell phone wants both phones to ring when the desk phone is called. Is this possible ? What is the proper description of this functionality.
Anyone got code samples they’d care to share ?

Thanks !

Randy,

Examples:

Dial(SIP/5551212&SIP/5551213,20,tr)
or
Dial(SIP/5551212&SIP/${EXTEN}@sip_proxy,20,tr)

The ampersand (&) separates the numbers to dial.