Currently I have an AT&T MobileShare.

I also have Sprint and use one of their MiFi devices for a computer that doesn't have a connection to broadband. It works fine, but of course I'm paying quite a bit for service.

I want to add another line to my MobileShare [and cancel the Sprint service]. Adding a MiFi is only $20 a month which is savings in itself. However as it's connecting a computer that I don't use (yes I'm paying for someone else's Internet):

I was wondering if there is an option to limit the amount of data that line can use in the MobileShare? I know I can turn off data at anytime, but that's pointless if the user goes over my limit because I'll get charged for that.

Obviously if I add an individual data only line, this would be easy to solve, but that defeats the point since I won't be saving any money (mainly because I only get 5GB on AT&T whereas Sprint is 6GB).

Thanks!