A lot of people are saying Apple will charge a monthly fee for the SOS service once the free service has expired. I am not so sure. First, while I am sure the service is not cheap, by most standards, it probably costs Apple very little compared to their overall budget. It is not like this service is being constantly being used. The satellites being used are mulitpurpose and SOS is probably only using a fraction of the bandwidth. The call center is likely a combined call center for other emergency services.
But, the bigger issue is the public perception. Imagine the first time someone tries to use the SOS feature and the can't get through because they don't pay for the service. Doesn't matter if Apple is right or wrong here (and they would be legally right), the bad press would overwhelming. Apple loves the good press it gets when someone is saved using this service.
About a year ago, VW was dragged in to a similar situation. Like many other cars, they offer a service to track your car if it is stolen, for a fee. Well someone had their car stolen with a child inside. The police tried calling VW to help track the car and got told that, since there was no active subscription, they would not help. Whether VW was legally right or wrong, they got a ton of bad press. As a result, all VW owners got 5 years of the service for free.