There are a few SMS services that are both free and safe to use, while others are not. Cryptocat is a good SMS program that works on both iPhones and popular Web browsers as of 2015, and it is free to use, according to Computer World.
Another safe SMS application is ChatSecure, which works primarily on iPhones and Android devices. Android device owners can add another application called Orbot to enhance the security of their SMS programs, explains Computer World. Additionally, applications such as Signal for iPhones or RedPhone on Android phones provide additional security for phone calls on smartphones.