First thing first, gather some things that you'll need.
Sorry, but the I forgot to take pics of the making, so all the pics here are of the finished product.
Also the quality of the pics is poor as I took them from my mobile. So bear with me.
Step 1: Gathering the Items
1) An old jeans (just it's back pocket will do).
3) Thread and needle.
4) Velcro strips.
5) Someone who can sew.
Step 2: Making the Mobile Cover.
Just cut along the stitches and remove the pocket. I've used jeans' pocket because it was of the right size and won't tear easily. Also I was not wearing those jeans.
Second Step : Making the cover.
For this just stitch both the sides of the pocket from the inside, so that when the cover is reversed then the seam will be inside.
Once sewed then stitch the bottom, but keep the seam of the side sides in the center, so than when reversed the ugly side seam is on the back.
Third Step : Attaching a flap.
Next we have to attach a flap on the top side of the cover so that it can be covered and also stop the mobile from falling out of it.
I took a flap from the same jeans and stitched it to the top side of the cover. The flap was big enough to cover the top.
Forth Step : Attaching the velcro
Last step is to stitch the velcro to the cover and the flap, so that it can be closed.