You mobile phone is always with you. It is very convenient to store in it some secure information, like passwords, PINs, ... But mobile phone can be stolen. And worst of all it can be stolen together with your credit card. You may imagine how excited the pickpocket will be if he found in your phone PIN code for your credit card. Cryptex midlet was designed to avoid such situation. Data you have entered in encrypted, somebody except you will be able to read it. How it is possible? When starting Cryptex you have to specify password (more precisely it is not password by encryption key used to encrypt data).
You can ask - is there any sense to store in Cryptex one password (or PIN) and protect it with another password. The answer is yes. You are not free to choose PIN code of your credit card and usually not able to use password you like for your account. And Cryptex allows you to specify any password you like and more over remember leading question for it, for example "Name of my dog", "Maiden mother's name", "My old phone number"... So it is unlikely that you will forget answer for such question and at the same time probability that other person can answer is very small.