I have created a web app to memorize numbers. It implements the mnemonic major system. The system works on the principle that it is easier to remember words/sentences/stories than numbers. The web app facilitates finding sequences of words that encode a number in the mentioned system. I called the app pinfruit.
My first take on implementing the system was incorrect. I simply associated digits to letters. According to wikipedia the mnemonic major system assigns digits to sounds, rather then the letters of the alphabet. And rightly so, I immediately noticed that it is easier to work with sound associations.
My mistake originated in that I first learned the technique in Poland, and in Polish it does not matter if you assign digits to letters or sounds because both correspond. Unfortunately, in English this is not the case, the major difficulty in learning the language.
I have used pinfruit to memorize mainly pins and phone numbers, but also bank site's user identifiers, which often come as numbers.
The trick is to create a memorable (vivid or absurd) sentence/story for a number. My old phone number: 07514590312, can be encoded with husky leader leaps midway Hanoi, school weather helps Madonna or sickly water leaps hometown. I refer you to the wikipedia article for the detailed description of the system.