mjoy - Free SMS
Here's how it works:
1. Sign up at mjoy.com using your mobile or PC browser. Initial registration asks for your country and mobile phone number.
2. You will receive a text with a special sign up URL, open it in your mobile browser and complete the registration process by choosing an ID and password.
3. Send your texts from within the mjoy mobile web app (2nd image). The person who receives the text will see that it came from your mobile number. A message reading "Text for FREE with http://mjoy.com" is appended to every message.
4. If the recipient replies to the message in the normal way, by hitting "Reply" in their phone's inbox, replying won't be free for them and if you pay for incoming messages it won't be free for you to receive either.
5. If you convince your friends to sign up for mjoy then you can text with them for free using the mobile web. Messages sent to mjoy members end up in their inbox in the mjoy web app (3rd image) rather than in the phone's SMS inbox. Web based mjoy messages can be of unlimited size and there is a nice threaded messaging interface