How to ship cells as a live culture?

Shipping cells to collaborators can be accomplished by either sending them a frozen aliquot on dry ice or by sending a live culture.  Sending a live culture has the advantages of the cells continuing their exponential growth to aid in timing of experiments.  This is accomplished by completely filling the flask with culture medium, closing the flask with a non-filtered cap and shipping overnight at room temperature.  The main disadvantages of this shipping method can be a leaking flask resulting in stoppage of the shipment or the shipment not reaching the destination prior to cell viability start decreasing.