I've written before about the new Japanese operator E-Mobile, that's been supporting VoIP on its HSPA network, via a data-centric device, with a client from Jajah.
It's now announced two more voice-centric devices, one a modified HTC TyTn II affectionately called the eMonster, and the other from Toshiba. Insofar as I can work out from the press releases, these work on "broadband voice" which I think is marketingspeak for VoIP.
Out of coverage areas, the phones' voice roams onto DoCoMo's network (for an extra fee). It's not obvious whether this means it hands over to circuit, or carries on using HSDPA.
(btw - if anyone more familiar with the product can confirm that it's using VoIP rather than circuit, please post a comment - thanks)