You have probably heard about google calendar's option for sending free SMS notifications about your calendar events.
Some time ago, while playing with google-calendar-data-api , I got an idea to write a program that would allow its users to send sms for free.
Sender and recipient both must have their google calendar account.
Recipient MUST set up her/his account for receiving SMS messages(This can be done in google calendar in "Settings->Mobile Setup") and then for receiving SMS notifications (in "Settings->Calendars->Notifications" check the "New invitations: SMS" checkbox).
So, how it works..
When a sender wants to send sms, she/he enters the text of the message and email address(es) of the recipient(s). Then the program, using google-calendar-data-api, tricks google calendar by creating an event (with no body, just the subject (text of the message)) and invites recipient(s) to that event (by sending the event notification to all email addresses user entered).
After that, the google calendar account of every recipient informs her/him about the event she/he is invited to by sending the sms notification which contains the event's subject.
And that is it.
Google Calendar becomes the free sms service :)
Of course there are some limitations.
Anyone can receive up to 20 messages per day, up to 150 per month. (Number of messages the user can send is unlimited)
The format of the message is: "SENDER'S NAME invites you to: MESSAGE TEXT @time and date"
The sms is sent by google, so my program can't do anything to format it.
The number of the characters for MESSAGE TEXT depends on the length of sender's name.
There are about 60 characters available in my case.
If your text contains more than that number, the program will split the text and create as much the events as necessary and send several sms messages.
The program (written in java) can be downloaded from here
You can't send sms to yourself.