string strPhone = "(!Phone!)";
            string strMobile = "(!Mobile!)";
            string strFax = "(!Fax!)";
            List<string> strMulti = new List<string>();


            //first build string

            if (strPhone != "")
            {
                strMulti.Add("Tel: " + strPhone);
            }
            if (strFax != "")
            {
                strMulti.Add("Fax: " + strFax);
            }
            if (strMobile != "")
            {
                strMulti.Add("Mobile: " + strMobile);
            }

return String.Join(" | ", strMulti.ToArray());