The new BlackBerries (8100 Pearl, 8300 Curve and maybe some other which I didn´t use) are prone to memory leak issues where email messages along with SMS & PIN get deleted for no apparent reason.
Rim released now a technote (KB13814) that this is a known problem. BUT at the moment there is no solution. Only some workarounds:
- reducing the size of allocated media memory to the lowest setting
- using a microSD memory card
- reboot the device after x days
More information can be found here (technote KB13814) .