send arabic sms shown as "????" at command ?

i found this code for connect and sms throw usb modem it works fine for english only - when i try to send arabic sms i got " ???? " in mobile so can any one help please ?

all code in class "clsSMS":
public void port_DataReceived(object sender, SerialDataReceivedEventArgs e) { try { if (e.EventType == SerialData.Chars) { receiveNow.Set(); } } catch (Exception) { throw; } } public SerialPort OpenPort(string p_strPortName, int p_uBaudRate, int p_uDataBits, int p_uReadTimeout, int p_uWriteTimeout) { receiveNow = new AutoResetEvent(false); SerialPort port = new SerialPort(); try { port.PortName = p_strPortName; //COM1 port.BaudRate = p_uBaudRate; //9600 port.DataBits = p_uDataBits; //8 port.StopBits = StopBits.One; //1 port.Parity = Parity.None; //None port.ReadTimeout = p_uReadTimeout; //300 port.WriteTimeout = p_uWriteTimeout; ...