RBOCS:
Regional Bell operating company (RBOC) is a term describing one of the U.S. regional telephone companies (or their successors) that were created as a result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983. The seven original regional Bell operating companies were Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Bell, Southwestern Bell, and US WEST. Each of these companies owned at least two Bell operating companies (Bell operating company). The BOCs were given the right to provide local phone service while AT&T was allowed to retain its long-distance service. The RBOCs and their constituent BOCs are part of the class of local exchange carriers (LECs). (Rhine, Robert S. March 2008)
ILEC:
An ILEC (incumbent local exchange carrier) is a telephone company in the U.S. that was providing local service when the Telecommunications Act of 1996 was enacted. ILECs include the former Bell operating companies (BOCs) which were grouped into holding companies known collectively as the regional Bell operating companies (RBOCs) when the Bell System was broken up by a 1983 consent decree. ILECs are in contradistinction to CLEC (competitive local exchange carriers). (Rouse, Margaret March 2008)
CLEC:
In the United States, a CLEC (competitive local exchange carrier) is a telephone company that competes with the already established local telephone business by providing its own network and switching. The term distinguishes new or potential competitors from established local exchange carriers (LECs) and arises from the Telecommunications Act of 1996, which was intended to promote competition among both long-distance and local phone service providers. (Rouse, Margaret March 2008)
MSO:
A multiple-system operator or multi-system operator (MSO) is an operator of multiple cable or direct-broadcast
References: http://searchunifiedcommunications.techtarget.com/definition/regional-Bell-operating-company http://searchunifiedcommunications.techtarget.com/definition/ILEC http://searchunifiedcommunications.techtarget.com/definition/CLEC http://en.wikipedia.org/wiki/Multiple-system_operator http://www.webopedia.com/TERM/I/ISP.html