BB Curve :: Phone Number Automatically Being Deleted?

I am using blackberry 8520 . i was having around 300 phone no. in my cell phone in first title got deleted automatically then again i saved title with name. Second time most of no. deleted from my cell now only 100 phone no. is there in my cell. retrive my no. i dont have any back up also. earlier i was not using BBM service in my phone but one of my friend is using that so i inserted his sim in my cell and set up my gmail and yahoo account in my phone. Now wats hapning to my phone that i dont know.