Looking at the relevant source files in FreeBSD 8.3:
@https://svnweb.freebsd.org/base/release/8.3.0/sys/dev/usb/usbdevs?revision=234063&view=markup:
vendor AIRPRIME 0x0f3d AirPrime, Inc.
….
vendor SIERRA 0x1199 Sierra Wireless
....
/* AirPrime products /
product AIRPRIME PC5220 0x0112 CDMA Wireless PC Card
....
/ Sierra Wireless products */
product SIERRA AC313U 0x68aa Sierra Wireless AirCard 313U
product SIERRA TRUINSTALL 0x0fff Aircard Tru Installer
Hmmm. The default mode should be VID:0x1199 PID:0x0fff and the target (modem) mode correctly 0x0f3d:0X68aa. However that's listed as 'Airprime' not sierra. u3g won't recognise that combination of IDs:
@https://svnweb.freebsd.org/base/release/8.3.0/sys/dev/usb/serial/u3g.c?revision=234063&view=markup:
U3G_DEV(SIERRA, AC313U, 0),
Thus I would guess it's switching it it from the default mode, Sierra VID and PID, but not assigning any serial ports to it because the result is not recognised.
In the FreeBSD 10 source a combination device exists:
@https://svnweb.freebsd.org/base/release/10.0.0/sys/dev/usb/serial/u3g.c?revision=260789&view=markup:
U3G_DEV(AIRPRIME, AC313U, 0),
I would expect this to work in pfSense 2.2.
Steve