Start with 2 strands of standard worsted-weight cotton yarn and #10 needles. These directions make a case approximately 6 1/2 inches long and 3 3/8" wide.

Directions:

Cast on 21 stitches. Work in seed stitch (k1, p1) until your work measures 6 1/2" long. Bind off.

I used the same yarn to stitch up the sides, then folded down the upper right corner and tacked it in place.

For the pink one, I added a tassel. For the other, I made a little medallion by casting one 1 stitch, then increased every row until I had 5 stitches, then decreased back to 1 and bound off. I sorta did that in seed stitch, but that doesn't work too well while increasing and decreasing. It still came out okay, however.

What's cool about this is that it could be made a little shorter for a cell phone or wider for a digital camera, so it has all sorts of possibilities.