When you memorized numbers that way, did you "see" the numbers in your mind's eye? And when you went to recall it, did you basically read it from that impression? I sometimes memorize numbers and other strings that way.
This mental phone book improved my ability to memorize other types of random strings. On one occasion I memorized a 20-digit hexadecimal license key, though I had to read it about three times. The client who watched as I keyed it in was very impressed. On a second thought it isn't that impressive given it's 12 digits short of a UUID.