Mobile telecom company with multiple agreements with mobile operators to send and receive data in and out of the operator's SMSC, acting as an intermediary between companies (i.e. content and brand owners) that want to interact with end users (through their mobile phones; i.e. via SMS) and mobile operators.
Since aggregators lack direct access into the SS7 protocol, SMS messages are delivered to the operator's SMSC, but not directly to the subscriber's handset. Instead, the SMSC takes care of further handling of the message through the SS7 network.