I used to think that M2, like all Memory Stick variants, is exclusive to Sony. That is, until I saw Memory Stick units made by different manufacturers.

Some handset models, such as the Nokia 6300, can handle up to 2GB of removable flash memory right out of the box. MicroSD cards are already available in as high as 8GB of storage, although SD cards at and beyond 4GB are already classified as 'High Capacity', and will only work with SDHC-compatible devices.