One of the limitations of Windows Phone 7 is, that Microsoft's new mobile OS isn't supporting user removable flash memory like microSD cards, as supported by Windows Mobile, but Windows Phone 7 uses embedded memory like Apple's iPhone does. However, this isn't a big deal as long as the Windows Phone 7 device in use has enough memory. As of today the ODM's memory size of choice seems to be between 8 and 16 GB (most of the recently announced Windows Phone 7 smartphones will have 16 GB anyway). However, even if Windows Phone 7 isn't featuring a customer swappable flash memory, it seems that some handset manufactures are using micro SD cards anyway.
While the microSD card is hidden on most Windows Phone 7 devices, it's not user accessible but it definitely makes sense for handset manufactures to use microSD instead of embedded flash memory. Flash memory can be pretty expensive and limited in stock while microSD is a bread and butter technology largely available today. And it has another benefit for the handset manufactures: They can easily upgrade the memory even within the device lifecycle or offering different customizations for different carriers and markets; for instance the HTC HD7 in Europe featuring 16 GB while the North American version features 8 GB only!
On the other hand, the Windows Phone 7 OS addresses the RAM memory and the internal memory as a kind of JBOD drive (Just a Box Of Disks/Just a Bunch Of Drives) where multiple physical memories (or drives) are combined into a single virtual disk. However, addressing memory this way doesn't provide any data redundancy (as known from RAID systems). As the name implies, disks are merely concatenated together, end to beginning, so they appear to be a single large disk and that's indeed the way Windows Phone 7 handles the memory. The flash memory of Windows Phone 7 isn't designed to be user swappable - all the flash memory is seen as one single drive and removing one part of the memory breaks down the whole device.
However, it seems that the microSD cards can be changed anyway, especially because the OS itself is part of the not removable ROM and therefore available even after a memory exchange. For the test, I've opened a brand new HTC HD7 (preproduction device) and replaced the preinstalled SanDisk 8 GB (Class 2) microSD card with a Samsung 8 GB (Class 6) microSD card.
On Windows Phone 7, this memory replacement requires a factory restore (hard reset) to initialize the new microSD card but even after several factory resets, it looked like it's impossible to change the microSD card and get the HD7 working again because the device always booted with the following error message:
However, after carefully putting the new microSD card into the microSD card holder again, the HTC HD7 finally booted and started with the Windows Phone 7 device configuration screen:
I haven't experienced any differences in speed or stability so it definitely seems that the new microSD card was fully accepted by the device (after the initial trouble). On the other hand I have to admit that I replaced a 8 GB card with a 8 GB card (even if both support different classes) and therefore it's yet not a proof that the HD7 will also handle 16 GB cards (which it should because some carrier configurations feature 16 GB) or even 32 GB microSD cards. Nevertheless, it definitely seems that a memory upgrade/change is doable and users might be able to easily upgrade the memory of Windows Phone 7 smartphones - as long as they know where the microSD card is placed.
However, at this point it's not confirmed that all of today's Windows Phone 7 devices will be indeed featuring microSD memory but it's yet just an assumption that most - if not all - will indeed use microSD. Furthermore it's not confirmed that all devices with microSD cards will accept the swap of the original memory card but there's a good chance that this is widely supported! Nevertheless, this topic definitely needs further investigations!
UPDATE: HTC just informed us that the commercial HTC HD7 isn't shipping with Class 2 microSD cards but something (not named) better. That's definitely good news but even it's even more interesting to know that (some?) Windows Phone 7 smartphones can also work with slow Class 2 microSD cards.
Cheers ~ Arne