I'm intrigued by the option to upgrade to premium for the cost of less than 1$, but the whole pay-by-mobile thing sounds... sketchy... I just want to avoid the "how did I fall for that?" moment when I see the bill next month.
Can anyone shed some light on this?
Obviously, the confirmation SMS isn't free- but how much? My MNO and boku are taking a bite too, but is that included in the original price, or will I get extra charges? Does pay-by-mobile even count for the purpose of upgrading to premium?

Any help from someone who used this option will be appreciated. Thanks!