Found this on another forum - seems to have helped me with the same problem!:

RIM has identified a design problem with the way that controls within the media application have been implemented. In the media options (”Media Application” > Pick an application such as Pictures > [BlackBerry Menu Key] > “Options”) there are two settings:

“Reserved Pictures Memory” – Default Value = 10 MB – This setting reserves memory for Pictures that the customer may take. It blocks off the memory, reducing the “File Free” amount that displays in “Options” > “Status”. This guarantees that the customer will have memory available and will not overwrite email messages within the memory setting set.

“Device Memory Limit” – Default Value = 20 MB – This setting is a safety water mark. It prevents the customer from placing more than the specified amount of memory in their content store (pictures, ringtones, music, etc.. in device memory)

The implementation problem with these settings is that the “Reserved Pictures Memory” setting does not prevent the customer from going beyond the specified amount of memory. That is to say, if the customer has it set to the default value of 10MB, they are not prevented from taking 15MB of pictures for example. The only setting that will limit them is the “Device Memory Limit” setting.

The 20MB default value for this setting is a bit high as typically after loading the handheld software, the memory available is about 20MB. If the customer has a number of contacts, calendar entries, tasks, memopad items, emails, etc… they could have less than 20MB available. This means, with the default settings, the customer could fill their content store to the point that Low Memory Manager activates in an attempt to free up new space by deleting emails and call logs. If approached by a customer in this situation, please recommend that they reduce the “Device Memory Limit” setting to it’s lowest value of 12MB. It is recognized that even this value is high, and the values (including the defaults) are being adjusted in future releases of handheld software.

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Having a large amount of images, ringtones and or games stored in the device may reduce available free memory. If the BlackBerry Pearl’s memory is at or near capacity the handheld will begin to delete the oldest Call Log and Text Message (SMS) entries in an effort to free up memory space. In order to prevent this, free memory must be increased.
NOTE: Saved messages will not be deleted.

Determine the Amount of Free Memory on the BlackBerry

* If the amount of free memory available on the handheld is 0, the amount of free memory must be increased to prevent the handheld from auto deleting call log entries and messages.

Suggested Ways to Increase Free Memory

Reduce Allocated Media Memory

1. Scroll to and select the Media icon.
2. Select the Pictures icon.
3. Select the Device Memory icon.
4. Press the Menu key, select Options.
5. Change the Device Memory Limit to 12MB.
6. Press the Menu key, select Save.
7. Hard Reset the BlackBerry.

Reduce Calendar Keep Appointments to 60 days or less

1. Scroll to and select the Calendar icon.
2. Press the Menu key, select Options.
3. Scroll to and select Keep Appointments.
4. Select the desired amount of time to keep appointments.
5. Press the Menu key, select Save.
6. Hard Reset the BlackBerry.

Reduce the amount of time Messages are kept on the handheld.

1. Scroll to and select the Calendar icon.
2. Press the Menu key, select Options.
3. Select General Options.
4. Scroll to and select Keep Messages.
5. Select the desired amount of time to keep appointments.
6. Press the Menu key, select Save.
7. Hard Reset the BlackBerry.

Clear Cache and Cookies

1. Scroll to and select the Browser or Media Net icon.
2. Press the Menu key.
3. Select Options.
4. Select Cache Operations.
5. Select Clear History.
6. Note: Clear History will no longer appear once it has been selected.
7. Hard Reset the BlackBerry.

Delete Unused Languages
Note: If deleting both the unused languages and the sample video wait to restart the device until both processes have been completed

1. Scroll to and select the Settings icon.
2. Select the Options icon.
3. Select Advanced Options.
4. Select Applications.
5. Scroll to and highlight each of the unused languages under the Input Support and Language and Input Support subheadings.
6. Press the Menu key.
7. Select Delete.
8. Select Delete.
9. When prompted to Restart select No until all unused languages are deleted.
10. NOTE:Repeat steps 4-8 until all unused languages are deleted then select Yes when prompted to restart.
11. Hard Reset the BlackBerry.

Delete Sample Video
Note: If deleting both the unused languages and the sample video wait to restart the device until both processes have been completed. The sample video is the pre-installed video for the blackberry and is ~2.2MB in size.

1. Scroll to and select the Settings icon.
2. Select the Options icon.
3. Select Advanced Options.
4. Select Applications.
5. Scroll to and highlight “Blackberry Sample Video”.
6. Press the Menu key.
7. Select Delete.
8. Select Delete.
9. When prompted to Restart select Yes.
10. Hard Reset the BlackBerry.

Change Call Log Options

1. Scroll to and select the Phone icon.
2. Press the Menu key.
3. Select Options.
4. Select Call Logging.
5. Select either Missed Calls or None.
6. Hard Reset the BlackBerry.

Hope this stuff helps some folks… additionally you could also delete the even log… I just saw something about this in another thread here and after posting I’ll go check out the instructions.