We have an old-type mobile with keyboard Sony Ericsson W715. I will try to rip in tomorrow how Estonian language has been presented there. The main characters are the letters õ,ä,ö,ü,š,ž, what are missing, If we are talking about Estonian SMS type keyboard.
As you can see on the screenshot in my previous post, I've added ä,õ, ö, š, ü, ž letters in my version;
if you'd like to test on your stb, NumericalTextInput.py with Estonian layout added attached...