They do not leave a voicemail if you don't pick up, but if you call the number, you get a voicemail for Venture Data Call Research, "one of the premiere data research" companies in the business. Despite the fact that they are in my own area code (in fact, the number puts them in a nearby town that I can walk to in about 15 minutes), it says "OUT OF AREA", but at least they don't mask their phone number.