A Samsung Focus document revealed that a microSD card when inserted into Windows Phone 7 is considered a ''permanent modification'' resulting in irreversible changes to card. A Focus FAQ page, states that once a card is added, ''it'll no longer be readable, writable, or even formattable on any other devices such as computers, cameras, printers, and so on''.
''This includes an inability to format microSD card for use in these devices.''
The page notes that even permanently removing a microSD card from a WP willn't make it useable in other devices again.
Microsoft itself gives a similar warning via a WP support page, where it's stated that once added, a microSD card becomes part of the phone.
''The WP7 treats the SD card as an integrated part of the phone. This's in contrast to other devices, where you can use an SD card to increase the memory available to device at any time or to transfer files to other devices.''
Meantime, AT&T has warned customers via Engadget that only ''Certified for Windows Phone 7'' microSD cards should be used in Microsoft's mobile devices. The reason, according to mobile carrier, is that WP platform ''requires a certified high-speed microSD card for optimal performance.''
At present, no such ''certified'' cards exist and no indication has been given as to when they'll hit store shelves. According to Microsoft support documents, certification comes down to more than just ''a simple matter of judging its speed class.''
''Several other factors, such as the number of random read/write operations per second, play a role in determining how well an SD card performs with WP7 devices.''
"The random access speed is the key factor in determining if a card is compatible with a WP, and the cards best suited to platform can reportedly only be bought in bulk by OEMs, leaving consumers between a rock and a hard place when it comes to beefing up the storage capacity of their WP."