1# Introduction to Telephony Kit 2 3Telephony Kit provides the following APIs that help you develop communication applications: 4 5- Call module: Allows an application to directly make a call and display the call on the application screen. A third-party application can start the system call application and redirect to the dialing screen to make a call. For details, see [Telephony Call Development](telephony-call.md). With the call module, the application can also format phone numbers and determine whether a number is an emergency number. For details, see [Call API Reference](../reference/apis-telephony-kit/js-apis-call.md). 6 7- SMS module: Allows an application to create and send SMS messages. For details, see [Telephony SMS Development](telephony-sms.md). In addition, the the application can obtain and set the SMS service center address, and check whether the current device can send and receive SMS messages. For details, see the [SMS API Reference](../reference/apis-telephony-kit/js-apis-call.md). 8- Radio module: Allows an application to obtain the name of the currently registered network, network service status, and signal strength. For details, see [Radio API Reference](../reference/apis-telephony-kit/js-apis-radio.md). 9 10- Data module: Allows an application to access cellular data services. Cellular data is a wireless network communication standard that uses the packet switch technology throughout data transmission and switch to provide voice, data, and video services for mobile devices. It enables users to use applications on mobile devices or browse web pages on the mobile network. For details, see [Data API Reference](../reference/apis-telephony-kit/js-apis-telephony-data.md). 11 12- SIM module: Allows an application to obtain SIM card information, such as the service provider, International Organization for Standardization (ISO) country code, and home Public Land Mobile Network (PLMN) number. For details, see [SIM API Reference](../reference/apis-telephony-kit/js-apis-telephony-data.md). 13 14 15## Constraints 16 17Before calling telephony service APIs, ensure that the device is equipped with a modem and SIM card capable of independent cellular communication. 18