1) Sony uses open source, they do like it. PS2 and PS3 could run Linux.
2) Sony-Ericsson already makes the Xperia line of Android phones. The Playstation phone is the same thing, with buttons.
3) Sony has another strategic partnership with Google Android in its new line of Google TV enabled televisions and Blu-ray players.
Sony may not meet your standards for always being in the spirit of open source. But they do use a lot of open source and have shown a heck of a lot more support for open source and open standards than other device companies.
Besides. Compared to the rest of the Android OS field, Sony fits right in. Take what you can get for free and don't give back any more than necessary.
PS2 Linux support was a massive joke -- they forced linux development to be perfectly orthogonal to the rest of the system, and I don't think anything that separates the PS2 from the typical desktop made it into open source (i.e., GPU drivers, and so on).
PS3 Linux support was retroactively revoked via firmwear update mere months after launch.
Datapoint re 1): the Sony Reader line is built on Linux. Not particularly open, though, since you can't modify anything. (There was some hacking done on the 500 and 505, but later models lack the firmware updater.)
