There are two different settings that can be pushed out by IT policy. One requires a password after a certain amount of time of inactivity (ie. if you scroll the track wheel once every couple minutes will reset the timer), and one to prompt you for a password after a certain amount of time regardless of if the BlackBerry is in use or idle (but not locked, cause well, that would be really dumb
If yours is after 30 minutes it asks for a password, even if you are currently typing on the BlackBerry, talk to your IT admin and see if they can change it to an enforced password and timeout (inactivity). This would at least stop the interruptions if you are in the middle of an email...Even if they set the timeout to be 2 minutes of idle time...
But if it's done for security reasons, there are a lot of places that will not deviate from their current plan.