There's actually no need to delete old emails and phone logs. Set how long you want to save messages for to a reasonable time period by going to Messages --> Options --> General Options, scroll down to the bottom and set "Keep Messages" to something like 3 months or less and you should be fine.
The place to keep an eye on every month or two is Saved Messages (if you use that function). These messages will NEVER be removed from the device until you manually delete them. You can use the View Saved Messages icon, or view them from Messages (View Saved Messages). I find I typically save messages that have attachments which (obviously) can take a lot of memory, so every month or two I view them and delete the ones I no longer need.
Other than that you shouldn't need to do anything. As with any computer, a reboot may be needed occasionally (if you abuse your BlackBerry like I do - constantly installing and uninstalling applications, overloading it with applications, etc). Of course, you can do this by simply removing the battery, but my BlackBerry's battery door was starting to get worn out until I found Soft Reset. A simple application that allows you to definatively reboot the device without having to remove the battery. You can install it Over The Air (OTA) by pointing your BlackBerry's Browser to:
http://www.geekandproud.net/blackberry-software/#SoftReset
And before everyone starts talking about using [Alt][Shift][Del] to reboot the device, this does typically work on a very clean device, but I have found it to be unreliable (the device looks like it reboots, but comes up without it being locked as it should) and sometimes even doesn't do anything. Soft Reset solves both of these problems.
Jerry
