How can I avoid the SMS fees sent from my software?

I am adding a notification feature to my users. I plan to connect it to the authorities in Sweden but I am required to be able to send all notifications as SMS.

This can be very expensive for me? How can charge the users for the service I am providing them. I only want to charge them for actually received sms notification.

Is there a smart way for me to not charge them but connect to their current service provider instead?

/DJ