disable data once used up

I have just received a text from O2 saying at as of the date of my next bill I will be limited to 1GB a month, and that last month I went over it. So I was wondering if there is a way to set the iPhone to turn off data once it hits 1GB worth of usage to prevent it going over the amount and being charged for it?

I am jailbroken so will also look any cydia add-ins.

 

oh I know you can manually disable your data using that, but I was thinking more along the lines of it being automatic once you hit your usage allowance / a preset usage, and it would automatically reset on your chosen date, ie the start of your new months allowance.