This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
reason is a read-only property that indicates the reason the call is being forwarded.
var reason = instanceOfMozMobileCFInfo.reason;
Return a number.
The value is equal to one of the
MozMobileCFInfo.CALL_FORWARD_REASON_* constant values.
Not part of any specification.