A subscription manager module or message processing engine operating within a messaging inter-carrier vendor (MICV) provides value added services to both service users (e.g., mobile telephone users) and service providers (e.g., information brokers, vendors, news sources, etc.). The MICV is disposed between a plurality of service users and a plurality of service providers and messages sent between these parties are processed by a subscription manager module, or message processing engine, which is configured to, among other things, manage short codes, detect undesirable spam messages, operate service user opt-in and opt-out processes, and perform billing functions.