Automatically disable cellular modem when phone is aleep?

I'm looking for a way to automatically have the cellular modem turn off when the phone is put asleep, and then turn back on when the phone is awoken.

I found out about SBSetting and SBSchedule, but from what I've read those seem to require manual toggling or do it based purely on time of day.

The reason for this request is that I have my iPhone running on a cheap prepaid plan where data is relatively expensive. The iPhone uses little amounts of data every hour (even when connected to wifi, plugged in, and asleep). I'd like to prevent this data usage when I'm not using the phone without having to remember to constantly disable data.