ctivity. Multimedia message service (MMS) sounds scarier because it is sending full graphic images from one wireless user terminal to another. MMS uses an Internet Protocol (IP)-based multimedia message switching center (MMSC) separate from the SMSC. Also, MMS sends its images as data files over packet data channels, so they do not go over the ANSI-41 signaling network. Active MMS subscribers may use a lot of CDMA resources, and we hope that they will pay for them, but their images do not use sig- naling resources. As we discussed in Sec. 25.4, SMS and EMS are special cases not only because they send subscriber data through the signaling network but also because there is no other, larger bit stream associated with these messages. For example, a sudden surge in cell phone voice calls caused by a major traffic accident will quickly fill the CDMA carrier's capacity with calls. Each of these calls generates some signaling activity, but the calls themselves use thousands of times more bits than the signaling messages. A similar surge in SMS and EMS messages also may fill the CDMA carrier, but now all the bits in those messages will be using the signaling channels. Heavy use of SMS and EMS will create one-for-one heavy use of the ANSI-41 signaling channels that we rely on for our system to operate. This means that SMS and EMS are signaling wildcards. The system operator can control the quantity of SMS and EMS messages by setting rates. If the signaling channel is getting full of messages, then we can raise the price to keep usage down. If demand elasticity favors a lower price with more SMS messages than the ANSI-41 signaling network can support, then it is probably time to increase signaling capacity. Different markets in different parts of the world have dramatically different SMS activity levels. As of the writing of this book, Japan is well known for the high volume of short messages on its wireless telephone systems, but the fad could catch on in other places as well. It is important for wireless system planners t