Phone design  

The seminal reseach work on...
The seminal reseach work on this subject is AT&T Bell Labs back in the 60's.
http://www.vcalc.net/touchtone_hf.pdf

Geez, James how'd you dredge that up?
I guess you can find anything on the web if you know where to search. It's interesting to me that the article doens't really define the perfect format. Several formats, both rectilinear and circular were good. What I do find interestes is the likelyhood that we ended up with the 3x3 format due to manufacturing ease. Guess that's no surprise.