Permissions

SMS 42 is a full SMS app. Android only lets the default SMS app receive, store and send messages, so the app asks to become the default SMS app.

PermissionUsed for
Default SMS app (SMS role)Receive incoming SMS, write them to the SMS store, show and send messages. Without it the app cannot work as a messaging app.
READ_SMS, RECEIVE_SMS, SEND_SMSShow your conversations, receive new messages, reply in a conversation, mark messages as read.
RECEIVE_MMS, RECEIVE_WAP_PUSHRequired from every default SMS app by Android. SMS 42 does not show MMS.
READ_CONTACTSShow contact names instead of phone numbers. Optional.
POST_NOTIFICATIONSNotify you about new messages. Optional.
Respond via messageSend a quick SMS reply when you decline a call (an Android requirement for default SMS apps).

Core functionality

Reading SMS is the app's core function: it is a replacement for the built-in Messages app that additionally recognises service messages (parcels, banks, bills, coupons) on the device. Messages are not uploaded anywhere; see the privacy policy.

Switching back

You can choose another default SMS app at any time in Android Settings → Apps → Default apps → SMS app. Your messages stay in the Android SMS store.