Problems with SMS: - it's best effort: message may (or may not) be delivered; they may (or may not) come in order; they may (or may not) be timely - SIM steal

Problems with SMS: - it's best effort: message may (or may not) be delivered; they may (or may not) come in order; they may (or may not) be timely - SIM stealing/swapping is not hard - it's all plain-text - if you fatfinger the phone number, your auth code goes to the wrong place