DTMF is actually 16 digits: 1 2 3 A 4 5 6 B 7 8 9 C * 0 # D. While most keypads don't have A B C D buttons, * and # are pretty much everywhere, and easy to dist

DTMF is actually 16 digits: 1 2 3 A 4 5 6 B 7 8 9 C * 0 # D. While most keypads don't have A B C D buttons, * and # are pretty much everywhere, and easy to distinguish, so adopting base-12 would be relatively easy.