// switch to the text mode
String atcmdresponse = atcommand.send("AT+CMGF=1\r");
System.out.println("Set TEXT-mode: " + atcmdresponse);

// provide the receiver number
atcmdresponse = atcommand.send("AT+CMGS=\"" + phone_number + "\"\r");
System.out.println("Set telephone number: " + atcmdresponse);

// provide the message text & confirm (terminate)
atcmdresponse = atcommand.send(text_sms + (char) 26);