Voice mail will certainly hamper your networking efforts occasionally. That's what he or she's there for. From the operator, you can learn whether the person you're trying to reach is on site or in Timbuktu. If there's an emergency, or at least a justifiable urgency, you can ask the operator to make sure your message is received. No. 17 of a system that isn't checked regularly.
Many systems assign numbers geographically, so that adjacent offices have sequential numbers.
Sometimes, your network target will be present, and receive a recorded message from you and a live one from the operator, but you still won't receive a prompt call back. Before you get angry or give up, view the situation from the contact's perspective. Your call is critical to you, but not necessarily to the recipient. To increase your chances of getting your calls returned, be sure to answer these questions when you leave messages. He suggested I do a little informal networking with you to get your views on the future of the widget-gidget industry and see if you know anyone at Transglobal Gidget I might ask about their strategies.