Sony has certainly made good on its word to make it easier for the developer community to build custom ROMs for its Xperia series of phones. To that end they have released some documentation, and the necessary proprietary Qualcomm drivers, to make it easier for those devs to get over the often-frustrating humps of building great custom software.
In a blog post outlining its intentions, Sony says that it is the first time they are collaborating with Qualcomm on its S3 lineup of chips (maybe because most new devices are going to be running S4) but this should make it easier to get bootloader-unlocked phones running the latest versions of Android.
The Xperia S is coming soon to Canada, but it will be released to the market with Android 2.3.6 Gingerbread. There are a lot of great features of the phone, but initial reviews have been harsh on the fact that it is running obsolete software. Hopefully this will allow developers to quickly iterate custom ROMs like CyanogenMOD 9 and MIUI so that we can enjoy some Android 4.0 before Sony releases its own version.