Re: 2fa choices
An alternative to SMS is to have the server make a voice call to the user, and accept a PIN from the user's keypad. DUO Security offers a system like this and given a suitable modem I think it wouldn't be difficult to do oneself. This also overcomes the objection that a phone number can be stolen (redirected to another phone) without stealing the physical phone, by social engineering the wireless company. Without the PIN, just receiving the call wouldn't authorize access.