Bill Angel allows users to keep track of their text, call and data consumption, and will alert them when they approach their monthly limit.
The retailer launched the app to tackle the £4.8bn wasted on unsuitable tariffs every year, and is hoping the service will usher customers towards a call plan more appropriate to their needs.
"Data use is continuing to skyrocket and more and more customers are now regularly overspending on their bill by exceeding monthly data limits," said Graham Stapleton, chief commercial officer of Carphone Warehouse.
"At Carphone Warehouse, we're committed to providing customers with independent impartial advice and have created the Bill Angel app to offer people a simple way to track their mobile phone usage, alerting them before reaching their tariff limits and helping them avoid additional charges."
Bill Angel is currently exclusive to Android device, available as a free download through Google Play. A BlackBerry edition will be released on July 7.
An iOS version is also in the works, but will only monitor data usage.