All options above will work remotely, in extension settings either wired or portable you have an option do do call forward, it has 2 sections, from co and from extension, set both the same, preset status on, fwd status availability on, fwd mode : fwd all. fwd destination = 9 + number

Also, make sure the extension is in a cos that allows fwd external

“I have not failed. I've just found 10,000 ways that won't work.”