Some suggestions and theories

[nablator]

A simple example of a polyphonic cipher: assume each letter of the alphabet is encoded by the next letter of the alphabet (so, A is encoded as B, K as L, etc) and in addition digits encode the following letters 0=A 1=E 2=I 3=U 4=O 5=S 6=A 7=O 8=E 9=I

This one is homophonic.