i know if use device and user mode, multiple phones can share the same extension, but all the phones are registered by the same account.
now i want multiple phones share the same extension, and all the phones are independently of each other. they just use the same extension number.
just like:
i have a extension number 2001 in two or more company（A and B and …）. but they can not influence each other. they just have the same extension number.