PCM works by storing data in small cells of chalcogenide, a special compound that can change physical states between crystalline and amorphous with the application of heat. It is "RAM-like" in that bits can be changed individually, not only in blocks as is required by NAND and NOR, yet it is non-volatile so power isn't required to keep the data in memory. This also means phase-change memory will be much more efficient as it doesn't need continuous power to function.
The Omneo P5Q PCM and P8P PCM are both 90nm, 128Mbit parts, with the first using the newer serial peripheral interface, and the second the older but more established parallel NOR. They are said to support one million write cycles, or around times more than the high-end, single-level cell NAND flash memory used in enterprise-class SSDs. That said, Numonyx still hasn't developed a NAND interface part and even when it does it believes PCM will compliment -- not replace -- NAND flash by acting as cache in the controller in order to speed I/O for data writes.
Numonyx did not reveal a suggested retail price, saying only that their products will have a premium over existing memory chips until volume ramps up.