We've been hoodwinked by trademark filing and domain registrations before (cough, BlackPad and SurfBook) so we wouldn't say this is anywhere near definite, but we just caught wind of a Sony Ericsson EU trademark registration for "Xperia Play," and SE PR firm Jung Relations has registered a variety of Xperia Play domain names, including XperiaPlay.com, .net, and .org. Yes, that certainly sounds like a promising name for the PlayStation Phone (although not quite as promising as, you know, "PlayStation Phone,") but honestly we wouldn't bet on anything at this point. We've got a feeling we'll either find out either at CES or at MWC in February -- hold on tight.
Update: Turns out SE also registered Xperia Arc, Xperia Duo, and Xperia Neo, so now our interest is definitely piqued. And our hopes are totally shatter-able.