You can check the full list of permissions of the particular app you use. Full permissions list is also available in Google Play - there's "permissions details"

You can check the full list of permissions of the particular app you use. Full permissions list is also available in Google Play - there's "permissions details" link at the very bottom (https://support.google.com/googleplay/answer/6014972 https://support.google.com/googleplay/answer/6014972). Personally, I check this list for every app I find interesting. If "read phone state" is listed then the app knows who's calling you, in a sense system feeds this data. Whenever the app uses it or not depends on how shady it is.