Once it's opened press the "Start" button. Now you can connect to your phone from a PC/Mac, with a browser (Google Chrome, Mozilla Firefox, Safari, etc...), just typing the provided URL (for example http://x.x.x.x:8080) in the address bar.
The cost of messages is that provided by your service plan (on the phone).
I hope you're enjoying WifiSMS and you'll support it.
For any problem, suggestion, or info you can contact me ("Menu -> About...").
Enjoy it! :)