I registered for the Sky TV mobile app and used my free code.
however, O2 have sent me another code to use. supposed to be for first 150,000 customers texting 'sky' to 2020 on o2 contracts.
the spare code is : X9EKAY7
make sure you hit RECALCULATE next to the code box for the code to be effective
Sky TV app only works on WIFI and not 3G
Installed fine for me, using my original code, but several people are having issues due to the high number of users trying to register.
But it all works fine, and 3 months free is great as there is no 12month tie-in!