Feature to use freeminutes

Hello @ all

I wish for me a thing, that i can have to example 3 trunks. Then i use 200 minutes from trunk 1 and then asterisk must use automaticaly the trunk 2. And when i use the next 200 minutes over trunk 2, then asterisk should take the trunk 3 and so one.

Is this feature possible?

For what i need this?
Exampe: www.lowratevoip.de, www.sipdiscount.com

Easy enough… could work nice with VoIP GSM gateways for LCR of a small company (albeit with lack of CLIP)… Will put it on the back burner and post back…