Please double check if Extras Devel is correctly added ( http://wiki.maemo.org/Extras#Extras-devel ) and activated. Then launch the app manager and choose download->all and then type "lock" that worked for me. If this still doesn't work: Download and install rootsh with the app manager and afterwards open x terminal from main menu and
type: "sudo gainroot" then press enter
type: "apt-get install call-locker" then press enter again
type: "Y" and press enter again

Don't type the quotation marks in though!