"The FCC's basic 911 rules require wireless service providers to transmit all 911 calls to a PSAP, regardless of whether the caller subscribes to the provider’s service or not." http://www.fcc.gov/guides/wireless-911-services/
Doesn't cover calling a tow truck, AAA, or a friend or relative to come pick you up. But if you only use the phone for real life-threatening emergencies, you don't have to pay.
The phone simply being turned on doesn't equate to more calls being made. Like the parent said, turn it on when you need it.
The $0.10 minutes that come with that aren't especially competitive with other prepaid services. I'm not sure they will activate a phone everywhere.
But the 'have a working phone' baseline isn't all that inconvenient or all that expensive.