AT&T tells Samsung Focus customers not to buy microSD cards yet, wait for 'certified' ones (update: random access speed is key)

We'd put forth the theory that Microsoft and Samsung would eventually certify microSD cards specifically for use with Windows Phone 7 devices after they finally came to terms with the fact that the microSD drama surrounding the Focus was going to lead directly to broken devices and broken hearts -- and sure enough, that's exactly what's happening. We just received this statement from AT&T, pointing out that the platform is extremely finicky when it comes to microSD selection -- so finicky, in fact, that only "Certified for Windows Phone 7" cards should be used. No such cards are currently available. Here's the full statement:

"Windows Phone 7 requires a certified high-speed microSD card for optimal performance. Because the Samsung Focus is expandable via a microSD card, only microSD memory cards certified for Windows Phone 7 should be used. This information is not currently marked on any microSD packaging in market today. As a result, we are advising customers to delay purchasing an external microSD card until the cards identified as "Certified for Windows Phone 7" are available commercially or in AT&T stores."

Coincidentally, we appear to have fried a card after moving it in and out of our own Focus today to the point that no PC, phone, or camera can read it anymore, so this is definitely a real problem that needs a real solution. It's odd that Microsoft appears to have been fully aware of this situation prior to release and yet AT&T's only now drawing the line, but we can't even imagine the kinds of bureaucratic head-butting that happens between corporations the size of AT&T, Microsoft, and Samsung. In the meantime, be careful out there, folks.

Update: The Focus is in the microSD hurt locker on at least two fronts here. First, the platform is definitely finicky in terms of card specification -- Microsoft's support docs explicitly say the requirements are more stringent than just the SD class:

"Determining whether an SD card is Windows Phone 7 compliant is not 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 Windows Phone 7 devices."

But what appears to have fried our card is the fact that any card inserted into a Windows Phone 7 device "will no longer be readable or writable on any other devices such as computers, cameras, printers, and so on" according to documentation on Samsung's site -- including, amazingly, the ability to format the card. That's hardcore, and it also explains why these guys are so skittish about external storage in general and why so few WP7 devices support it at this point.

Update 2: We've just been slid some more details on the specs Microsoft is looking for to certify cards -- turns out it has a lot to do with random access speed, not total throughput, as the company's support docs imply. It's the latter value that's identified by a card's class (the big number that's often stamped on the card), so that's why Microsoft can't just say "any card Class 6 or higher is fine" or something to that effect. What's upsetting is that we're hearing the cards that work best can't be bought by consumers -- they're only sold in bulk, which probably explains why the cards installed in the Focus are fine and nothing else is (at least, according to AT&T) at the moment.