From its first appearance, SOC (Security Operations Center) was created for MSS (Managed Security Services). At 2002, when I tried to dig information on SOC with Google for the first similar project at China, I found the top matches came from ISS and its subsidiary organizations (ISS had 6 SOCs worldwide then), such as ISSKK, and its Taiwan agent – ISSTW.,but this was not my target.
Another significant description of SOC is from NTT. NTT built up its SOC to provide MSS service to their customers! ie. Security can be sort of value-added service, besides being competitive advantages. See the following diagram on NTT's SOC:
ATT, BT, MCI and other famous telecom operators are rolling out various MSS services to their customers, though no diagrams are found at the Internet. I summarized the MSS products by those telecom operators at a previous post in Chinese, for example, MCI, bundled with NetSec, provides MSS services like management of firewalls, IDS devices, anti-virus systems and PSS services like security risk assessment, policy maturity accessment and even application lifecycle assessment.
Security vendors are other kind of major players at MSS market. Besides ISS and Symantec mentioned before, see one diagram from Verisign:
Nowadays, you can search out more reports on SOC, both for internal security operations and MSS.