I set my reminders as 5 or 10 minutes for example. Yes I've done a battery pull as I've had my BlackBerry for many weeks and have never once had a calendar reminder audio or visual notification. My alarms however do work.
My BlackBerry is basically as standard from factory as supplied by o2uk. Only basic apps installed like Facebook, Windows msgr, Flickr, Viigo. I've checked all my profile settings and calendar options to no avail :(
Hmm, looks like 184.108.40.206 is the latest OS available from O2 UK.
So you next option is to install an OS from either another carrier or a beta version. (You can check the Sticky post at the top of this forum concerning "Beta OS".
The 9000-Bold forum has a sticky post with a link to the latest official OS release, if you download that OS and install it to your computer, the next step is to search for a file called "vendor.xml" once you find it delete it. Once you delete that file plug in your Blackberry and run the application loader it will prompt you to upgrade.
Note: To play it safe (As I typically do) perform a manual backup before upgrading the OS)
8830 -> 8330 -> 9550 -> 9650
Just think about how far BlackBerries have come from then till now... And what else is coming.