Here's another good site with brining info.
http://cookshack.com/barbeque_guide/101 ... c528293334
His spin on brining frozen poultry is...
"Question: Can you brine a frozen bird?
Answer: No. The brine and osmosis won’t be able to work on a frozen product and if you let the bird since in a salty solution longer than recommended, you’ll have a less than good quality bird – mushy and over-seasoned."