I would guess that the person who is trying to make the call may have their VOIP phone number in an area that the toll free number has blocked. A number does not have to be in an area where other number like it may be. I know when I was working on a project in the US Virgin Islands we had a 202 area code number at a managers desk, had no idea why it was still there, but he said it was installed in 1970 by then ITT and was never removed, that is one long FX, but I'm sure US NPA's are in other parts of the world.
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