public class DMDBModule : IDisposable
{
    private static DMDBModule fModule = null;
    private SqlConnection fConnection = null;
    private string sConnString = "";

    public static DMDBModule DataModule
    {
        get
        {
            if (fModule == null)
            {
                fModule = new DMDBModule();
            }
            return (DMDBModule)fModule;
        }
    }

    private DMDBModule()
    {
        XmlDocument doc = new XmlDocument();
        doc.Load(WebConfigurationManager.AppSettings.Get("appsets")); // Загружаем общий файл настроек

        sConnString = doc.DocumentElement.SelectSingleNode("descendant::connstr").Attributes["connection"].Value;// Строка соединения
        fConnection = new SqlConnection(sConnString); // Организуем пул соединений
        ...
    }

    public string getConnectionString()
    {
        return sConnString;
    }
...
}

...
public class PhoneList : System.Web.Services.WebService {

    private dsHelpDeskTableAdapters.spGetPhoneListTableAdapter taPL = null;

    public PhoneList () {
        if (taPL == null)
        {
            taPL = new dsHelpDeskTableAdapters.spGetPhoneListTableAdapter();
            taPL.Connection.ConnectionString = DMDBModule.DataModule.getConnectionString();
        }
    }
...