Default [Q] Unlocking Japanese Phone (au KDDI)

I recently returned from Japan with a smart phone. It is a Kyocera Digno S (model KYL21) and my service provider was KDDI au. When I cancelled my plan with au I asked if they could unlock my phone but they had no idea what I was talking about. Now that I am back in the US I want to use my phone with a local service provider.

Are there any companies or services in the US that can unlock a phone? Or better yet, is there anything I can do to find my phone's unlock code?