I got an answer this morning that solved my problem:
To prevent Web robots from attacking the gateway with standard login/password “root/root”, default password is built using the last 6 characters of the board ID : pdmk-$serialno.
For example, if an iFemtoCell has 704BEc1234AB as board ID, then the root password will be pdmk-1234AB (case sensistive).
This last 6 characters can also be retrieved within the host name displayed in the shell prompt:
klk-wifc_1234AB login: root