In 1967, the first toll free (800) numbers became available.  The 800 prefix was in use for over 30 years, until the available numbers started running out.  Since then, 888, 877, 866 and 855 prefixes have been implemented.  Each subsequently released toll free prefix has approached complete utilization even faster than the preceding one!  Based on this trend, it is very likely the new 844 toll free prefix will sell out shortly after it becomes available to the general public, on December 7th, 2013.