Since many sites now allow (or even require) 2-factor authentication, it's a good idea to use an authentication app on your smartphone to get the security code. This is a much more secure method, because codes texted over SMS could be intercepted. There's also the danger of SIM cards being duplicated or even hijacked with some creative social engineering. The Authy app for iOS or Android is a good option, because it sends a secret number and combines it with the time of day so the code changes after 30 seconds. Authy also will keep all of your codes for all of your accounts in one central location, which is convenient.