I got it sorted. I had to change the sources.list for the apt-get command. It uses the same as the included App manager. Since I use the Faster Application Manager, a different sources.list is used by this app. I had to add the fremantle extra repository to the standart app manager and then to update via apt-get update and then to issue the downgrade as described above. Yeaaah. I can send SMS now again without costs.