Having recently made a 110-digit POA system, I naturally wanted to test it out, so I began by memorizing the 17 numbers of everyone I work with. Basically I chose a memory palace and populated it with images. Right away, though, I noticed that the POA system works best with multiples of 3 or 6, whereas a phone number is 10 digits. I solved the problem by making the first Person of each locus the actual person whose number I was trying to remember.
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It worked well enough, but I suspect there are still more efficient ways. I know memorizing lists of 10 digits is a very common memory task. How do you guys memorize phone numbers and such?