Many Android devices are smartphones, but so far, we haven't talked about how to program applications that use phone features. In this chapter, we will show you how to send and receive Short Message Service (SMS) messages. We will also touch on several other interesting aspects of the telephony APIs in Android, including the Session Initiation Protocol (SIP) functionality. SIP is an IETF standard for implementing Voice over Internet Protocol (VoIP) by which the user can make telephone-like calls over the Internet. SIP can also handle video.