There's a region free firmware upgrade you can find on the AV forums, it works well on my 3910S.
One caveat - it is the version 5 firmware upgrade. There is a version 6 upgrade out since November, but not a region-free one (yet). If your 3910 is already up to version 6, I would not recommend using this region-free firmware. Also, if you use this firmware and then get the version 6 (without region-free), it will erase your region free. So:
1. If you have version 5 (not region free) on your 3910, you can get the firmware (region free) from AVForums. Then don't upgrade to version 6, at least not until a region free version comes along.
2. If you have version 6, I think the only thing you can do is wait until a region free version comes along.
Hope that helps!