There is an option at my provider to "load" the PIN directly to a device. That would eliminate a need for a higher security, but it would also bring up a privacy concern, 'cuz you will be disclosing your phone # to me. Given that, do you think you woulds still use that option?
You've had the ability to load directly to a mobile # (without the refill code method) and you've been holding out?
I personally tend to prefer the method that protects privacy but simplicity (load directly) trumps privacy concerns for most.
From a mobile, not having to go the refill code route would be preferable and easier for most. If you can offer that, it probably should be the default even (and refill code as the optional method).