iOS 4 and greater supported multitasking for some specific use cases:

• A program needing a limited amount of time to finish a task (such as uploading a file) and can be suspended after that. It would not be woken up until the user went back to the app.

• Playing audible content to the user while in the background, such as Pandora.

• Recording audio while in the background

• Keeping the user informed of their location, such as a navigation app

• VoIP apps like Skype

• Newstand apps which update content occasionally

• Communicating with plugged in accessories (added in iOS 5)

• Apps which communicate with Bluetooth devices (added in iOS 6)

iOS 7 adds two additional use cases for multitasking.

• A program can register that it wants to download small sets of information regularly. For example, it could download twitter updates regularly. This new API allows you to specify that you'd like to be woken up to download information every so often. For instance, a program could say it wants to download information after it's been asleep at least fifteen minutes. The system will then try to find a time where it can wake up as many apps at once to do their work. Minimizing the number of times the device wakes up will help it save battery.

• A program can register to be woken to download content if it receives a remote notification. The idea is that it can download the content and be ready to display it if you go into the app.

The directory you're looking for happens to be /var/wireless/Library/Preferences. This is where the Settings > Cellular settings are stored. The per-application settings are stored in the database /var/wireless/Library/Databases/CellularUsage.db. If you want to add a setting manually, you'll need to add an entry for the application in two tables. The first is bundle_uuid, and you'll need to set the bundle_id field to the friendly bundle name (such as com.developersbliss.Helicopter), and then the macho_uuid field to its UUID (such as DD314675-0AA8-8A84-DB2BB966BAD8) (Repeat this step for each UUID that the application has. In my particular example, there are two UUIDs. Just add another entry to the table for each UUID, but with the bundle_id set the same as before, and with the macho_uuid set to the next UUID the application has.). Then you'll need to make an entry in the bundle_info table with the bundle_id field set to the friendly bundle name used in the bundle_uuid table, and then the flags field set to 0. This will make that particular application be restricted from using cellular data. To enable the application to use cellular data again, just set its flags field in the bundle_info table to 1. Any application not found in this database is assumed to be allowed to use cellular data.