IMPORTANT - Let's say you are smart and you use your phone for 2 step SMS authentication but, you can still be vulnerable because of "Number Port-out Scams"

“You may not know this has happened until you notice your mobile device has lost service,”. “Then, you may notice loss of access to important accounts as the attacker changes passwords, steals your money, and gains access to other pieces of your personal information.”

Identity thieves can   “port” your mobile number out to another provider.Once in control of the mobile number, thieves can request any second factor that is sent to the newly activated device, such as a one-time code sent via text message or or an automated call that reads the one-time code aloud

Fraudsters can call a customer service specialist at a mobile provider and pose as the target, providing the mark’s static identifiers like name, date of birth, social security number and other information. Often this is enough to have a target’s calls temporarily forwarded to another number, or ported to a different provider’s network.


https://krebsonsecurity.com/2018/02/how-to-fight-mobile-number-port-out-scams/