The dispatch system is different at Landstar Express America. While Qualcomm is occasionally used to announce loads (not offer, announce), agents most often call with load offers. They are located in offices around the country and each has his or her own phone number(s). Dispatch is decentralized so no single ring tone would work.
In the Year-plus we have been with Landstar, we have done business (hauled freight) with over 30 agents. Most often, they call us before we call them. It is not at all uncommon for an agent we have never worked with before to spot us on the board and call with a load.
In a decentralized dispatch system like this, the appropriate ring tone for all incoming calls would be "Who Are You?" by The Who.