get current system volume level on iPhone

musicPlayer = [[MPMusicPlayerController iPodMusicPlayer];

currentVolume = musicPlayer.volume;

This is now deprecated as of iOS8.0 so try the following

#import <AVFoundation/AVAudioSession.h>

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
CGFloat volume = audioSession.outputVolume;

Celestial.framework has an AVSystemController class that lets you get and set the current volume. Unfortunately it is a private class so Apple won't accept it in App Store submissions

If it helps, you can abuse the public MPVolumeView class a bit: http://www.stormyprods.com/blogger/2008/09/proper-usage-of-mpvolumeview-class.html