Why is my iPhone 4 randomly deleting some of my contacts...?! Does anyone know..?

[reallytanswimchickt]

For some really strange Reason some people are no longer listed in my phone..like my mother or some of my close friends numbers are all gone..I find it very strange.no one was on my phone an I certainly didn't do it..if you have any idea why this could be please help !
Thank you in advance! 10 points best answer
Also I looked it up online but found no similar questions to mine..now I find it hard to trust my phone