[mpyne]

I don't think they can be, as I don't have a Twitter account.

Certainly I would be pissed beyond belief if I tried to login to my bank (assuming they ever pull their heads out of their asses to support 2FA) and couldn't because I don't have cellular service in addition to Internet.

[gamacodre]

I already have this problem; both my bank and my credit union introduced 2FA but only with SMS. Once enabled, any attempt to log in using a not-yet-authorized browser or app is stalled until I get that text message. Presumably a call to customer service would sort it out eventually, but that prospect isn't terribly pleasant.

[krrrh]

Every time I have to call customer support to reset a bank password it makes me realize how bad of a security hole most phone support is. Security through two-factor authentication is only as strong as the process for bypassing it.