I've bough my daughters a Windows Phone each, just before Christmas, both on a cheap contract (in the UK). The phone contract allows upto 100Mb of data download per month. On their older Android phones it was possible to download an app that would monitor and limit their download's every month to just 100Mb, ensuring they didn't go over their limit and be charged for it.
You guessed it! Is there anything similar for Windows Phone (7.5)?