Long time no hear! This was because I had nothing new to report. I did nothing new with Open USB FXO and I did not have the slightest idea why my prototype failed to work.
I still do not have the slightest idea. However, in a private conversation with one of the blog readers, I was convinced that letting people take a look at my work could help in spotting the error in my design, whatever this error is (this statement makes the funny assumption that the number of errors my design accounts to just one).
Therefore, I created a google code project for Open USB FXO. It can be found at http://openusbfxo.googlecode.com/, and the sources can be browsed at https://code.google.com/p/openusbfxo/source/browse.
Please do not take the correctness of any of the uploaded files (schematics, boards and libraries) for granted. They are uploaded just for public scrutiny and review, in the hope that someone else can spot this error that I cannot see myself. Hopefully someone will.