Try your own:
You have 2 EditTexts as,
EditText ed_to;
EditText ed_message;
Before using following code, initialize EditTexts using findViewById()
String to=ed_to.getText.toString();
String message=ed_message.getText.toString();
SmsManager sms = SmsManager.getDefault();
sms.sendTextMessage(to, null, message, null, null);
Update: While using above code, you have to set permission
<uses-permission android:name="android.permission.SEND_SMS"/>
This will not show you the compose message window, instead, directly send sms.
If you don't want to set permission and want to see compose message, use following:
String to=ed_to.getText().toString();
String msg=ed_message.getText().toString();
Intent smsIntent= new Intent(Intent.ACTION_VIEW);
smsIntent.setType("vnd.android-dir/mms-sms");
smsIntent.putExtra("address", to);
smsIntent.putExtra("sms_body",msg);
startActivity(smsIntent);