Since I now have a new Mobile-Internet-Contract (with HSPA) I decided to upgrade to the latest Build 134.
The "pkg image-update" ran for 2h. The only Issue I had after the Update was BUG 12380. I could not connect via putty from my Windows-Machine. But after using the Workaround in Comment 3 (adding "clone:ptmx 0666 root sys" to the File "/etc/minor_perm"), all was well.