fallback alert service

Hi,

Maybe this is already possible, or it's a feature request for the next release. Anyway, I'd like to have some kind of fallback alert method in case the used alert service is down. E.g. if I need to be alerted through a sms2email gateway which is down, it should use the next sms gateway. I figured it would be simple if the same dependency system could used for this purpose.

Thanks,

Joost