We first took a look at Data Monitor for BlackBerry 10 in early 2013 (on video) and for those of you that don't have an unlimited plan it may well be the difference between additional carrier costs or not.
After a recent update Data Monitor is now headless and the developer has kindly given us 100 free copies to give away. As always; you'll need to be quick though as they'll be snapped up within minutes.
As the name of the app suggests it will record how much data your BlackBerry is using and will even warn you when you are at 50%, 75% and 90% of your monthly allowance. Within the settings of the app you can enter the amount of MB's per month you have to use and there are toggles to turn off the warnings if you like, although I think that would kind of defeat the object.
If you're quick enough you can get Data Monitor for free by following these instructions:
Hit up the app in BlackBerry World
Pull down from the top bezel and select 'Redeem'
Enter the code DATAMO2014B and the price will switch to free
Data Monitor for BlackBerry 10 is normally priced at $0.99 if you miss out on the redemption code but still want to download the app.