This code snippet may be simple but I spent couple of hours to get things done.On my searching I learned the difference between SPFieldUrlValue,SPFieldType.URL and SPFieldLink.
Simply,I wanted to add the "HyperLink" column to my existing ContentType.
SPWeb web = SPContext.Current.Web;
SPContentTypeId cId = new SPContentTypeId("0x0100AF98B284ECB44322916F1A1AD1A9E31C");
SPContentType cType = new SPContentType(cId, web.ContentTypes, "MurugesanCType");
web.Fields.Add("T2", SPFieldType.URL, true);
SPField f = web.Fields["T2"];
f.Description = "Type your Org NAme";
web.ContentTypes[cId].FieldLinks.Add(new SPFieldLink(f));
web.ContentTypes[cId].Update();