The word has come down that Hitachi has stopped making its Wifi SIP handsets and is exiting that line of business. If you liked any of their phones you may still be able to get them from retailers existing inventory, but numbers are expected to be limited.
I had one of their first offerings, the WIP-5000 model, back in the summer of 2005. It was a really nice piece of hardware. I paid almost $400 for it and was really hopefully that it’d be a good cordless solution for my office.
It suffered issues with its early firmware, but those may have been overcome through ongoing development. One big issue that made it unworkable for me was it simply would not generate enough volume. If there was any noise at all around me I just couldn’t hear the other party. This lead me to use a wired headset with it for a while.
There were other issues as well. Battery life was very poor and the phone would get warm when in use. Documentation was poor. The cordless range was very short. Faced with these issues I eventually resold it on E-Bay. It was a cool device, but too limited to be practical.
They had later models which I’m told some people like a lot. Myself, this early experience with VoWifi is what drove me into evaluating SIP/DECT solutions when they started to become available.