Have you heard of anyone losing a phone memory card and that by accident? Or perhaps you have personally experienced it?
I have a girlfriend who has taken some shots of an important family function and when she was ready to download the pictures, found the memory card missing. She has no idea when it had gone missing.
It is a good thing that memory cards are easy to replace but unfortunately, memories captured on film (for lack of a better term) are irreplaceable.
If you are dependent on your cellphone for picture-taking, you may want to take extra precaution because I hear some cellphones have weaker design in the area of memory card storage.