Thanks for the help, I have no Zimlets deployed, but searching the forum I found this topic
Zimbra Mobile Installation Guide
Then I issue :
zmprov mc COSname zimbraFeatureMobileSyncEnabled TRUE
and the Sync with my blackberry now work.
I don't know if before launching the above command the feature was enabled, but after, the synchronization starts working.
Also I found a very useful list of commands to see what features are enabled by account.
Zmprov Examples - Zimbra :: Wiki