Update docstrings for VoicemailContract to be more descriptive.
Update docstrings for VoicemailContract to be more descriptive.

Bug: 21343781
Change-Id: I221f61d4e9306a92c736a12b2cff3d9fccebdc47

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base