It depends on the service you use. Many services do require some form of payment. These usually fall into a couple of categories. Some will require little to no payment up front, but you'll incur cost each time you actually track the phone. Some require a bigger up front payment, and have a specific quantity of free monthly uses. Some may be free completely, but usually have very limited features. Both Android and iPhone have a number of applications available. There are also windows based utilities that are available.