According to the Nikkei, Softbank Mobile, who owns Japanese PHS provider Wilcom, has developed a handset that connects to both standard mobile and PHS networks. At the earliest, it will be introduced in June. The addition of PHS allows for inexpensive voice communications.
The maker is Kyocera and it will be loaded with some version of Google's Android.
PHS devices in Japan have 070 prefixes. Taking a look at Wilcom's pricing, you'll see that the standard plan is ¥13.125/30 seconds, which is about half the price of NTT Docomo's Value SS plan (¥21/30 seconds).
However, nearly 30 yen per minute is still expensive, relative to the rest of the world.