WARNING:

You need write permissions on the USB device to make it work properly.
Consider adding your user to the operator group:

% pw groupmod operator -m jerry

and adding a rule in /etc/devfs.rules like this one:

[system=10]
add path 'ttyU*' mode 0660 group operator

To load this new rule add the following to /etc/rc.conf:

devfs_system_ruleset="system"

Then restart devfs to load the new rule:

% service devfs restart