Android: Ever needed to recharge earlier than expected because you've run out of data? Avoid this in the future by using My Data Manager, a free app that will alert you when you get close to your free data threshold.When installed it keeps track of your plan type (monthly or pay-as-you-go), amount of data included per month, and the 1st day of your billing cycle. You may also set your plan's roaming details. From then on it will log your use of mobile data, roaming mobile data, and Wi-Fi data used. You can set up notifications for each of the three categories when they hit a certain amount of data.
One small drawback - the app will not work if moved to an SD card. It only takes up 1.1MB of space, so this isn't a big deal for most users.
My Data Manager is a free app with ads displayed for Android 2.2 or better. You can also buy a pro version without ads for $3.92.