[lovamova]

If they add a first factor (4 digits PIN code) and this as a second factor, then I think we have a winner. The PIN code will protect you from insecure networks, losing your phone, theft and it's easy to remember.

The PIN code is a weak link, but doesn’t do much without your phone. Your phone is a weak link, but you won’t get the SMS without the PIN code. Chained together they’re almost stupid and fail proof.

[diminoten]

I think folks overestimate a) how often physical theft actually takes place and b) the level of sophistication that folks who steal your phone are going to have.

In order for me to use the "thing I have" to get into your account, I'd need to know your account. The number of targeted thefts that take place are really low, compared to the number of folks who run around with "password" or "letmein" as their "thing they know".

The threat model for Joe User is just not that complex, is all I'm saying. For Paranoia User, options should certainly exist, but for her brother Joe, it's not very necessary.