This code snippet changes the template on the request if its a mobile

MobileHandler.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using umbraco;
using umbraco.BusinessLogic;
using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Core.Services;
using Umbraco.Web.Routing;

namespace PROJECTNAME.Web.Mvc.Mobile
{
	public class MobileHandler : IApplicationEventHandler
	{
		public void OnApplicationInitialized(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
		{ }

		public void OnApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
		{
			PublishedContentRequest.Prepared += (sender, args) =>
			{
				if (IsMobile(sender as PublishedContentRequest))
				{
					// Check to make sure the request is valid
					var request = sender as PublishedContentRequest;
					if (request == null || !request.HasPublishedContent || !request.HasTemplate) 
						return;

					var node = request.PublishedContent;

					// Gets current Template from request
					var template = applicationContext.Services.FileService.GetTemplate(node.TemplateId) as Template;

					// Get mobile template
					var mobileTemplate = applicationContext.Services.FileService.GetTemplate(template.Alias + "_Mobile");

					// change requested template to the mobile one
					request.SetTemplate(mobileTemplate as ITemplate);
				}
			};
		}

		public void OnApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
		{ }

		private bool IsMobile(PublishedContentRequest sender)
		{
			if (sender == null)
			{
				return false;
			}

			return sender.Uri.AbsoluteUri.IndexOf("://m.") >= 0;
		}
	}
}