They're not spoofing callerID. It's easier than that: They just have a PBX with 4-digit as extensions mapped to the XXX-XXX-???? block. Their PBX (voip or trad

They're not spoofing callerID. It's easier than that: They just have a PBX with 4-digit as extensions mapped to the XXX-XXX-???? block. Their PBX (voip or traditional) does all that callerID magic. Since they don't have direct-dial numbers in that range, it will work. Why? This way they can see easily in their logs how many calls start at a given minute, and check that the phone company is billing correctly their calls.