What difference does it make if a phone is unlocked?

Usually when u have an unlocked phone it means u can go to another network than the one branded on it..usually you won't be able to browse the Internet or send mms messages becus the settings are those of he branded network but therebisna quick fix for that you just have to change the port numbers and apn for the specific network u want and sometimes u can't access features like the store or homepage because it is set for the previous network