phone_number_editText = (EditText) findViewById(R.id.phone_number_editText);
        sms_content_editText = (EditText) findViewById(R.id.sms_content_editText);
        send_sms_button = (Button) findViewById(R.id.send_sms_button);
        
        send_sms_button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
            String phone_number = phone_number_editText.getText().toString().trim();
            String sms_content = sms_content_editText.getText().toString().trim();
                if(phone_number.equals("")) {
                   Toast.makeText(MainActivity.this, “No”, Toast.LENGTH_LONG).show();
                } else {
                    SmsManager smsManager = SmsManager.getDefault();
                    if(sms_content.length() > 70) {
                        List<String> contents = smsManager.divideMessage(sms_content);
                        for(String sms : contents) {
                      smsManager.sendTextMessage(phone_number, null, sms, null, null);
                        }
                    } else {
               smsManager.sendTextMessage(phone_number, null, sms_content, null, null);
                    }
                    Toast.makeText(MainActivity.this,"OK", Toast.LENGTH_SHORT).show();
                }
            }     
        });

<uses-permission android:name="android.permission.SEND_SMS">