There are a lot of voices available for iOS 7...

gistfile1.cs

      var ss = new AVSpeechSynthesizer();
  		foreach(var voice in AVSpeechSynthesisVoice.GetSpeechVoices())
			{
				var su = new AVSpeechUtterance("Microphone check. One, two, one two.") {
					Rate = AVSpeechUtterance.DefaultSpeechRate,
					Voice = voice
				};

				ss.SpeakUtterance(su);
			}