Most of the “Unknown” callers with the “Unknown” caller ID are telemarketers. But, I have found that some are field service inspectors. These are field service inspectors who have “limited” cell phone minutes and they do not want anyone calling them back on their cell phone and using their limited minutes. I know this because sometimes they will leave a voice message and ask for a call back at a later time on another number … probably a landline or a voice-over-internet telephone line such as MagicJack.
At SOFI, we do not answer calls from the “Unknown”. These are time-wasters. You should follow this same principal.