"out of pocket" (= not reachable)

[Kim & Rima McKinzey]

>...As an attorney who's worked for many years with New York law firm lawyers,
>investment bankers, etc., I can tell you that "out of pocket" to mean "not
>available" has been used in these circles for years. I have heard almost
>daily. No one seems to remember that it originally meant "lacking money."

I, too, was surprised the first time I heard out of pocket meaning
unavailable/unreachable - and I grew up in NYC, so either all these
bankers, et al. came from somewhere else or ?  The first time I heard
it used this way was from my Oklahoma born and bred mother-in-law.
I'd previously only heard meaning having to pay for something
yourself, not lacking money.

Rima