I suspect the carts are 'very' locked down. I just signed up and I'll start getting charged when I insert my special 'instant ink' carts. i.e. The printer (and

I suspect the carts are 'very' locked down. I just signed up and I'll start getting charged when I insert my special 'instant ink' carts. i.e. The printer (and therefore HP) will know when I've put in the magic ones they've sent me (and they'll send replacements when these are detected as being low). I guess converse should be possible though - if I put in regular commercially bought carts, these shouldn't come off my print total.