Utility class to render MVC Partials & Actions in WebForms (or server side controls).

control.ascx

<% WebFormMvcUtil.Html.RenderAction("Index", "PhoneNumber"); %>

WebFormMvcUtil.cs

namespace Website
{
    using System.IO;
    using System.Web;
    using System.Web.Mvc;
    using System.Web.Routing;

    public class WebFormMvcUtil
    {
        private static HtmlHelper html;

        public static HtmlHelper Html 
        { 
            get
            {
                return html ?? (html = new HtmlHelper(CreateViewContext(), new ViewUserControl()));
            }
        }

        public static ViewContext CreateViewContext()
        {
            // get a wrapper for the legacy WebForm context
            var httpContextWrapper = new HttpContextWrapper(HttpContext.Current);

            // create a mock route that points to the empty controller
            var routeData = new RouteData();
            routeData.Values.Add("controller", "WebFormController");

            // create a controller context for the route and http context
            var controllerContext = 
                new ControllerContext(
                    new RequestContext(httpContextWrapper, routeData), 
                    new WebFormController());

            // find the partial view using the viewengine
            IView view = 
                ViewEngines
                .Engines
                .FindPartialView(controllerContext, "RenderActionPartial")
                .View;

            // create a view context and assign the model
            var viewContext = 
                new ViewContext(
                    controllerContext, 
                    view, 
                    new ViewDataDictionary(), 
                    new TempDataDictionary(), 
                    HttpContext.Current.Response.Output);

            return viewContext;
        }
    }

    internal class WebFormController : Controller
    {
    }
}

Simpler and clearer and works with MVC 3

Idea to create HtmlHelper came from http://stackoverflow.com/a/4247959/444244