Store programs should not be able to place random phone calls nor hidden sms messages. All those things that can cause costs to end users should basicly open sailfish sms and phone applications, and end user needs to manually press send or call button.

But of course if you sideload root suid applications while in developer mode, then $RANDOM_NON-STORE_NATIVE_APPS can cause you costs by sending hidden smses. (Android apps cant make hidden phonecalls nor sms messages).