This document compares short codes and long codes for SMS messaging. Short codes are 5-6 digit numbers leased for $500-1000 per month that allow scalable and regulated 2-way messaging. Long codes are 10 digit numbers that are free but cannot scale and are not regulated, putting messages at risk for blocking. The document recommends short codes for critical, time sensitive alerts due to their speed, scalability and low risk, while long codes may work for non-critical messages with lower speed and message cost requirements.