I have seen some Android apps on my phone require this android.permission.READ_PHONE_STATE permission. I don't know if I could trust them. I know this permission will give the app access to many information. I'm particularly interested in what functionality in an Android app normally require the information like DeviceId , SimSerialNumber, SubscriberId?
Phone state provides access to a lot of information about the phone. Usual usages will be for reading the IMEI of your phone and your phone number. This can be useful to identify you in their systems.
It can also be needed if the application is made compatible for Android 1.5 or lower, because this permission didn't exist back then and is added automatically by the play store to those apps
Another possible reason is so they can mute audio events if you're in the middle of a call. This is why apps like Pandora, Spotify, etc need the permission - so they can mute themselves when you get a call.
Not long ago I discovered that for some devices you should add android.permission.READ_PHONE_STATE if your application sends SMS. Probably in some cases SmsManager tries to retrieve some information about phone state before sending sms.
For example getting exception for HUAWEI GRA-L09:
java.lang.SecurityException: Requires READ_PHONE_STATE: Neither user 10174 nor current process has android.permission.READ_PHONE_STATE.
at android.os.Parcel.readException(Parcel.java:1543)
at android.os.Parcel.readException(Parcel.java:1496)
at com.android.internal.telephony.ISms$Stub$Proxy.s! endMultipartTextForSubscriber(ISms.java:1224)
at android.telephony.SmsManager.sendMultipartTextMessage(SmsManager.java:404)
来源：https://stackoverflow.com/questions/19966864/what-kind-of-android-application-will-require-android-permission-read-phone-stat