In Android code, how can you retrieve the IMEI number of a phone by using the TelephonyManager class, and what permission is required?

Introduction / Context:
The IMEI is a hardware identifier for many mobile devices. This question assesses understanding of how to access telephony information on Android using the appropriate API and permission. Although modern Android versions restrict access to identifiers more strictly, the traditional pattern still appears in interview questions and legacy code bases.

Given Data / Assumptions:

• We are writing Android application code in Java or Kotlin.
• The goal is to retrieve the IMEI number of the device, when permitted by the platform.
• We know that telephony information is exposed through the TelephonyManager class.

Concept / Approach:
TelephonyManager provides access to telephony related information, including the device identifier on devices that expose it. To use this manager, code calls getSystemService with Context.TELEPHONY_SERVICE and casts the result to TelephonyManager. Older code commonly called getDeviceId, while newer APIs offer getImei on some devices. Access to these identifiers is protected by the READ_PHONE_STATE permission and subject to additional privacy restrictions on newer Android versions.

Step-by-Step Solution:
Step 1: In an Activity or other Context, call getSystemService(Context.TELEPHONY_SERVICE) to obtain a TelephonyManager instance.Step 2: Cast the result to TelephonyManager so you can call telephony specific methods.Step 3: Ensure that the application declares the READ_PHONE_STATE permission in the manifest and, on modern Android versions, requests it at runtime.Step 4: Call getDeviceId or getImei on the TelephonyManager to retrieve the IMEI or a similar device identifier, handling the possibility that the value may be null or restricted.Step 5: This sequence matches the description in option B.

Verification / Alternative check:
Android development guides show examples that use TelephonyManager for device identifiers and mention the READ_PHONE_STATE permission as requirements. There is no documented method that reads IMEI from Settings.System or Build.SERIAL directly. This confirms that option B describes the correct high level approach for legacy scenarios where IMEI access is allowed.

Why Other Options Are Wrong:
Option A is incorrect because Settings.System does not expose a standard device_imei key and is not the recommended mechanism for hardware identifiers. Option C is wrong because IMEI values are not stored in arbitrary files on external storage; that would be insecure and unreliable. Option D is incorrect because Build.SERIAL represents a different identifier and does not always equal the IMEI, especially across different device manufacturers and Android versions.

Common Pitfalls:
Developers sometimes assume that IMEI access will always succeed, ignoring privacy changes that may return null or require additional user consent. Another pitfall is failing to handle security exceptions when the permission is missing. Modern best practice is to avoid relying on hardware identifiers whenever possible and use more privacy friendly identifiers or server side accounts instead. However, understanding legacy APIs remains useful for maintaining older applications.

Final Answer:
By obtaining a TelephonyManager from Context.TELEPHONY_SERVICE and calling getDeviceId or getImei with the READ_PHONE_STATE permission granted.