I've got a UC540 configured with an incoming call plan to send all calls to Ext. 521, which is normally forwarded to Blast Group pilot number 511.  The customer wants to be able to occasionally forward all incoming calls to an external number, which, I presume, means temporarily changing the 521 forward to the external number, then back to 511  They are using SP504G phones and, so far, I can't figure out an easy way for them to easily do this.  Each phone shows its own extension, and the shared line for 521, but call ofrward on the phone seems only to work for the main extension.  Can anyone help?