According to FierceVoIP:
The current ooma device has a 450 Mhz ARM processor onboard running Linux [and] a derivative version of Asterisk...
ooma has released their modifications to Linux, per the GPL: http://www.ooma.com/linux/
I wonder if ooma has purchased a commercial license for Asterisk? If not, I believe they must release the source code mods they've made to Asterisk as well.