When I see this number on my caller ID, I just don't answer my phone. May as well stop calling! If I don't recognize a phone number or the number looks suspicious, I ignore it! When I see the words "unknown", "unavailable", or "restricted", I ignore that as well. I know the numbers of all my friends, family members and business partners and those phone calls are the only ones I answer.
Could be just a computer profiling when you are home and when you are not.
This information is valuable to telemarketers/solicitors as they don't waste
their valuable time. (Your time isn't considered valuable)
At any rate, they are nothing but a bunch of (uncleanly illigitimates!)