You can have as many accounts set up as you want, and you can get information about multiple phone numbers on a single Optus account.
Click here to see Phone Usage on the App Store.
A quick and easy way to view usage information for your internet or mobile account on your iPhone.
As soon as it's open, Quick Usage will display usage info from the last time it updated, and start automatically refreshing the info as well.
Quick Usage supports one account only. For multiple accounts, use Phone Usage.
Click here to see Quick Usage on the App Store.
See if your service provider is compatible with these apps on the support page.