I've created a small app for iOS where you can check your remaining data, text messages, calls and see how much your next invoice is going to be. It supports TouchID, 1Password integration, and has a widget. I need to iron out some details. For example we thought we might show a breakdown of rollover data, extra bought data, and data included in this month's plan. However figuring out how to derive those numbers proved to be a bit trickier than anticipated :)
I made it and I have it running on my phone since around November but I haven't had time to upload it to GitHub and since I'm not sure about any legal issues around it I haven't published it to the App Store or anywhere else. I need to figure out how best to distribute this for people to use.
Meanwhile here are some screenshots.