Unity editor extension to increment iOS build number after each build.

AutoIncrementBuildNumber.cs

using UnityEditor;
using UnityEditor.Callbacks;

public class AutoIncrementBuildNumber
{
	[PostProcessBuild]
	public static void OnBuildComplete(BuildTarget buildTarget, string pathToBuiltProject)
	{
		if (buildTarget==BuildTarget.iOS) {
			PlayerSettings.iOS.buildNumber = (int.Parse (PlayerSettings.iOS.buildNumber) + 1).ToString();
		}
	}
}