Figure 3 illustrates the architecture in supporting mobile text messages using the SIRP model. Each mobile phone service provider will deploy one or multiple text message servers (TMS). When a user sends a text message to another user (who may be with another provider), the text message is stored in the sender provider's TMS, and only the message header (including the corresponding phone number and a message id) is sent to the receiver provider's TMS. The receiver provider's TMS will notify the receiver about the message header. If the receiver wants to read the message, the receiver provider's TMS will retrieve the message from the sender provider's TMS on behalf of the receiver.
Asynchronous voice messages are currently supported by cell phone service providers, where a recorded voice message is sent to a receiver, or a group of receivers. This service can be potentially exploited by spammers given its capability to send a voice message to a large number of receivers with relatively little effort. Moreover, as the service is being integrated into VoIP based applications, it becomes even more attractive to spammers. This service can be supported using the SIRP model instead of the sender-push model essentially in the same manner as mobile text messages. We skip the detailed discussion due to space considerations.