It probably sends a non-premium message too then. There must be some kind of check in the network so that it's not possible to charge someone just by knowing their number.
No check, Premium SMS technically doesn't require any opt-in. Charging on SMS receipt is called "MT billing" [1] and this is how PSMS works in most countries including the US. PSMS is heavily regulated but the nature of the business today makes it unattractive for anything but fraud.
That's an eye opener. Should be trivial to enforce this on a network level (requiring user initiation), but I guess that is not something network providers would just implement on their own.
I wonder why the app requires SMS write permissions though.
App stores like Google Play should reward apps which require the least amount of permissions by pushing them higher in the search results (and publicize that fact).
