I've checked the posts and it is unclear if wi-fi is disabled through firmware or not. This has happened before with the Sprint Mogul where the phone had GPS but was disabled through firmware. When the phone was updated from Windows Mobile 6 to 6.1 the GPS in all Moguls became active - so it is possible.
I just found a post about an unlocked C905a where in the review by the customer at the bottom of the article he talks about the phone having Wi-Fi.
"I have been tried to switch the batteries between the two new c905a phones. It seems one of the battery something wrong. It did not get fully charged. I talked to AT & T, they will ship to me a new battery.
The good battery will last through the day if no WIFI on. With 100% at 8am, I will get about 40 to 45% left at 8pm with several calls and 20 to 30 minutes play card game which I consider ok as a basic phone."
http://www.unlockedphone.biz/sony-ericsson-cyber-shot-c905a-8-1-mp-camera-phone-silver-2/