After several days I "solved" the problem:
Either pfsense or the WRAP board is very sensible about long cables (My old router - linksys WRT54GL - worked with the same configuration perfectly).
| telephone socket – 1m cable -- Modem -- 20m cable -- WRAP board
does not work properly. In my case the connection came up, but pfsense was not routing any traffic (do not ask me why).
| telephone socket -- 20m cable -- Modem -- 1m cable -- WRAP board works smoothly.
Just in case someone has the same problem...