I have two 7961 phones.
Phone A Line-1 extension - 1000
Phone A Line-2 extension - 2000
Phone B Line-1 extension - 3000
Phone B Line-2 extension - 1000
Now some one calls extension 1000 and phone B picks on second line. Aftre that he transfer call again to extension 1000 and this time phone A pick it on line 1.
After transfer is completed Phone B can not see busy line status for extension 1000.