How can I determine the phone's voicemail number in Android code?
You can use getVoiceMailNumber() in the TelephonyManager class, please note that this may not work with all cell phone providers:
Call getVoiceMailNumber() on the TelephonyManager.
来源：https://stackoverflow.com/questions/5518817/how-to-determine-the-voicemail-phone-number-in-android