Disappearing SMS/MMS/E-mail/Call Log reason for it. You’re running out of Device Memory;
According to  below steps save your bb

Closing Open Applications
ALT+Escape/Back Key
Make sure you haven't left applications open.
There should be 5 applications that are always open.
Default 5: Phone, BBmessanger, Browers, Homescreen, and Call Log(if mobipoker reader installed,it be appeared)
You may have other 3rd party applications that may have to run in the background, but most can be closed.

Auto Delete ON/OFF
Under Messages:
Select Menu/Blackberry Button
Select Options
Select General Options
Keep Messages: (Shortest is 15 Days, Longest is Forever)

Battery Pull
Pull out battery and leave out for 30 Seconds.
(I do this at least once a week) Just for safety and memory leaks.

Check How much free memory you have
Options -> Status -> File Free: XXXXXXXX Bytes
Make sure it's not low.

Clear Event Log
Press ALT + LGLG
Menu/Blackberry Button
Select Clear Log

Clear Browser Content Cache
Open up your Browser
Menu
Options
Cache Operations
Clear Content Cache

Delete unwanted Applications to free up Device Memory
By using your Desktop Manager, and Application Loader
uncheck unwanted Applications also unused Language Packs

Thanks for this! I just had this happen to me a few days ago and I almost cried!

Nice post!!

And this will happen if SMS/MMS/E-mail/Call Logs disappear... mmm... saving messege... you never know when this can come handy.... :P... peace...

thankssssssssssssssss

Thanks for this!

Thanks for this!

Thanks for your guide.
I just do it.
Great!