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A telephone call originated from an alternate number in order to disguise the caller's identity and/or intent.
"Jimmy tried to skate on me for a month of utilities and wouldn't call me back, but I finally bagged him with ninja digits from the conference room line at work."

"Have you heard about the new iPhone app that throws ninja digits? Dude, you can call from any friggin' number you want!"
by Slithorex March 08, 2010