FWIW in the last 2 years, the text message for a charge authorization never failed.

The only time it was somewhat tedious was in China, where google voice app does not work on a local connection (but mine is set up to forward messages to email, so all it took is a few extra seconds of wait until the email comes through).

IMO C1 is better in that sense than Chase or Citi (both of which I canceled precisely because they were next to useless overseas due to overzealous "fraud protection"). Knock wood, hope C1 does not follow.