On some questions here on SOverflow I found THIS. But it says that it is not avaiable at the moment and probably it will never get avaiable.
Based on THIS I realised that there is no need on building my own SMS service.
So the question:
My java application has to send SMS messages to users and receive SMS messages from users. Do I really need to pay some SMS gateway or is there some free SMS GATEWAY (with some limitations ofcourse) that I could use to test my application?
Simplewire Kit looks really simple but the demo examples are failing because I don' have Simplewire account. Simplewire documentation says that there is a 30-day trial for sending SMS. But this is for two way:
"For 2-Way, demo credits are not available because you will need your own mobile number hosted on Simplewire’s Network. Simplewire supports 2-Way numbers for many different countries and area codes. Please contact Simplewire for more information."