You can install this free antivirus application for android. It allows you to be safe to install applications that try to subscribe to premium services or can make calls to numbers with additional cost.
This antivirus scans every application you install or you have already installed on your smartphone with hardly any consumption of resources or anything battery. Detects threats related charge calls without your consent.
It will notify you of those applications likely to be able to make a scam.
You can also avoid additional charges on your bill and eliminate those applications that do not trust with a simple touch.