An abbreviation for “Responsible Organization” which is the term for an organization or entity which has access to the SMS 800 database. There are around 300 resporgs. They would be “registrars” in the domain name terminology. Many phone companies are Resporgs but not all phone companies are Resporgs and not all reporgs are phone companies.
We have a whole section of our site for information on and related to Resporg. See http://www.tollfreenumbers.com/resporg/