Memorize numbers using the Major System. The chart at sweetscape.com tells you how to convert numbers to letters and then make words.
Remember this chart. This is the only memorization you need to do. Use the helpful hints such as n=2 and n has two down strokes, m=3 and m has three down stokes, for easy memorization of this chart.
Use the consonants only to form your words. Use vowels to fill in and make the word. For example, 404 would be "rsr" so your word could be "riser". This would work well if the number relates to an early riser.
Practice converting numbers you need to memorize into short words and phrases related to them using the letters associated with those numbers.
Add humor whenever possible. Pick a word that brings out something humorous about the person to which the number relates. For example, if you remember your pin number at your bank with the phrase "more dough", every time you go to the bank picture the ATM spitting out thousands of hundred dollar bills at you. The more outrageous your visualization the easier it is to remember.
Exaggerate a feature about the person, place or thing the number relates to, for easier memorization. For example, you may use "big nose" to remember the phone number for your friend who has a large nose, and then imagine that nose getting bigger and bigger until it fills up the room.