The rest of this chapter covers telephony-related classes in the internals package that only PhoneApp uses, android.internal.telephony. This package is layered over an implementation of telephony internals for a particular telephony technology, such as GSM or CDMA. That layer, in turn, communicates with a Radio Interface Layer (RIL) that is implemented as a daemon in Android.
Figure 15-1 shows the architecture of the Android telephony system. PhoneApp supports an Intent that enables other applications to start phone calls. The Telephony Manager is available through Listeners, as shown in the previous section.
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