PHS is a mobile data network that has been around for a long time in Japan. W-Sim is a universal module for PHS that can be used for Notebooks, in mobile phones or with PDAs.

The Will Com W-Sim measures 25.6x42x4mm and only weighs 10g. Transfer data speeds are 128kbps. The antenna is inside the module. A 600kb storage allows users to store 700 phone numbers.
Will Com also announced a tiny mobile phone that can be used with the W-Sim. See photo below.
More details and photos on K-Tai Watch Impress (Japanese) and on the Will Com site (Japanese).

3G Foma would actually be the faster and newer alternative to PHS, but it looks like there is still a market and room for innovation in the PHS area.