Lots of Android apps are designed to run--and sometimes even boot up--in the background. That's part of the reason why many Android users employ task-killer apps--to keep unnecessary apps from running in the background and wasting memory.

Having lots of apps running in the background also leads to unnecessary cellular data usage. The easiest thing to do is to make sure that your phone doesn't sync with servers unnecessarily; do this by navigating to Settings, Personal, Accounts & Sync, and turning the automatic syncing feature off. This change will ensure that apps like Gmail, Twitter, and VZ Backup Assistant aren't constantly connecting to the Internet and downloading the latest mail/Tweets/contact info. Instead, you'll have to manually download these updates.

You can take things a step further by blocking your apps from accessing cellular data networks while they are running in the background. You can use a free app like to block apps from using data, but there's a catch--it works only on . However, if you , you can install DroidWall and control which apps are allowed to access your cellular data network.

Both and have hinted about introducing shared data plans--possibly with rollover megabytes--but we've yet to see anything concrete. While we wait for these mythical plans to come about, we can (sort of) simulate them with some clever tethering tricks.