Bilal,

if you are using .NET 3.5 Service you need to set maxReceivedMessageSize at the binding configuration. You will have experience problem sending huge string due to default DOS attack protection

  <binding name="WSOrderForService" maxReceivedMessageSize="2147483647">
          <readerQuotas maxDepth="2147483647" maxStringContentLength="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" maxNameTableCharCount="2147483647" />
        </binding>