The question of expandable storage for Windows Phone 7 devices has been going back and forth ever since the OS was announced. Originally we were told that there would be no expandable storage. Once hardware rumors started rolling out we were puzzled by the included micro-SD card slots. At the Windows Phone 7 Launch, the Samsung Focus was out in broad daylight showing off its expandable storage via micro-SD. Even HTC’s HD7 is in on the secret, though the card is harder to get access to.

We get a little more clarification this morning courtesy of Paul Thurrott of the Windows Supersite (and the upcoming book: Windows Phone Secrets). According to Thurrott, the micro-SD expansion capability isn’t officially supported by Microsoft, but is a carrier option. He adds that this was never intended to be something that a user does on their own, and that there are technical reasons why you shouldn’t just drop any random memory card in your phone. Apparently using low quality micro-SD cards can lead to major performance and stability issues.

The recommendation from Microsoft’s Charlie Kindel is to have this done by your carrier and there is a very good reason for this. This is something that the carriers are supporting; so if there is a problem, you should be able to get it taken care of by your carrier.

Does this make you think twice about getting a device like the Samsung Focus? Give us your thoughts in the comments.