You are required to choose the subscription plan to start. Subscription plans are designed feature-wise suiting to needs of the organizations of varying size and structures. All plan options have unlimited users.
Screen-Magic is an ISV partner of Salesforce.com. SMS Magic app is listed on Salesforce AppExchange. It is native app and the installation is fairly straight forward.
You need to first Sign Up and choose a subscription plan. You can either purchase the subscription or avail the free trial for 15 days. All the features mentioned in subscription plan will be available during free trial. You will be provided 10 credits for testing. If you need more, you can purchase trial SMS pack or contact our sales team. We can also provide an incoming number for testing. Please reach out to firstname.lastname@example.org if you need it.