If you call early in the morning, around lunchtime and at the end of the day, you are more likely to catch your contact at his or her desk and avoid the "gate keeping" assistant. If you do not have the direct number, try using the company's automated phone directory. Call a digit up or down and after apologizing, ask to be transferred to the person's direct line. Make friends with the assistant and try to get him or her to arrange a good time for you to call.