Think of it as the prepaid cellphone of the tolling world. Shortly before Labor Day, the Department of Transportation introduced E-ZPass On The Go, slipping hundreds onto convenience-store racks at Massachusetts Turnpike rest stops.

Inside the clear packaging, consumers find the same transponders previously available only by mailing, faxing, or submitting an online application to the Massachusetts Department of Transportation, or by enrolling in person at a Registry of Motor Vehicles branch or one of three dedicated E-ZPass customer service centers.