SMS send from within an app seem impossible to detect?

Question

I have just created a cool app that work with SMS. I would like to say to my users: don't worrry, my app send SMS but you can track them in your favourite SMS application.

I don't want them to be afraid that I will overload their monthly fees.

So, the way I send SMS is very simple:

SmsManager sms = SmsManager.getDefault();
sms.sendTextMessage(phoneNumber, null, position, pi, null);

And that is very fine.

Unfortunately, all sent SMS does not appear in any SMS application, so user doesn't know that a SMS has been send.

Yes, of course, I could create a list in my application that shows send SMS, but the user won't trust me.

So I am very afraid that SMS send within app are totally invisible and there is no way to track them from the end user side.