I bought one of these from Play for £11.99. It came with an adapter to convert it to a Memory Stick Pro.
The 4Gb card works great in my Orange(UK) locked Sony W200i for past couple of days. I used a PC with card reader to read and write my MP3 files to the card.
I did have early reservations about whether the card was counterfeit because the labelling was different towhat is shown on SanDisk's website. The metal part of the adapter was also slightly different. It was made in China.
But the blister packaging is identcal to a SanDisk Cruzer I bought from elsewhere and both quote a SanDisk Ireland address for tech support.
I've not had any issues with the Cruzer or my new M2 card, so I am quietly confident they are genuine.
Ironically, the 128Mb M2 card that I pulled from my W200i is made by SanDisk Taiwan, and the labelling again is different - a SanDisk logo appears to the right of the words 'SanDisk'.
So buy this M2 card with confidence.