Anyone care to provide a primer?
The class of speed measurement we are referring to is the official unit of speed measurement for SD Cards, defined by the SD Association. The Class number represents a multiple of 8 Mbit/s (1 MB/s), the least sustained write speeds for a card in a fragmented state (Class 2, 4, 6) or the minimum non-fragmented sequential write speed (Class 10).[17]
These are the ratings of all currently available cards:[14][24]
Class Speed
Class 2 2 MB/s
Class 4 4 MB/s
Class 6 6 MB/s
Class 10 10 MB/s
I mentioned the faster speeds as unnecessary for a cell phone because these faster speeds of Class 6 and 10 are pretty much reserved for high-speed SLR cameras that need a large "pipeline" to transfer single frame images at multiple frames per second. Our phone doesn't take multiple frames of still images per second. (Quite the opposite. The Epic 4G Touch probably can't take more than one shot every two or more seconds.)
Interestingly, video imaging has no requirement for high data transfer speed. This is because the "pipe" for video isn't used to resupply an entirely new images every second. Most HD video images are "ghosts" or rendered images of the previous frame and therefore don't completely rewrite the previous image.
For example: A DSLR that has the capability to fire off several shots a second will actually be noticeably faster if it has a higher class memory card, because the faster card allows the camera to save image data at a much higher rate than a slower card would. With the higher class card, the camera doesn't have to pause and wait for its buffer to empty before taking more pictures, it just keeps shooting. The difference here is that your typical Android phone isn't likely to put that big a load on the write capabilities of its memory card.
Most of the time that you spend waiting for a picture to be saved on a phone is usually the phone processing the image, not saving it.
A typical Android phone's Micro SD card might be a Class 2, meaning it's guaranteed to write at 2MB/s. Most companies actually make the cards to exceed that expectation, sometimes by quite a bit. If you take huge amounts of pictures with your phone, a Class 4 Micro SD card, which is just one class higher, might benefit you. It won't exactly be a life-altering experience, but it could speed things up if your phone's camera takes pictures at something higher than 5 Megapixels. That is the reason I suggest you buy at least a Class 4 card, because the E4GT takes photos at 8 megapixels.
If you use the USB Storage feature of your Android phone pretty frequently, then things are a bit different. When plugged into a computer as a USB storage device, the full capabilities of the card are used to transfer data
