All the product launches I have been to have been relaxed about what you where - thought most of the time half the crowd is dressed in their retail uniforms. I suspect if they have invited you they won't want to make you feel bad for under dressing :)
So a t-shirt and jeans would be fine, a shirt and pants would be fine too. No need to bother with a suit.
The Xperia Z was the standout smartphone of CES in Vegas this year. Chatted with one of the Sony USA staff about it on the NZ Tech Podcast last month. I'll be at the event too so do come and introduce yourself.