There dozens of sites for sending free online sms worldwide. Most of them are ugly websites with tons of ads, looks like they are built in 5 minutes. But the service works. I follow them, after sometime they shut the service down, something happens. I don't know why, and I'm not sure how do they do it.<p>In most of countries SMS is very expensive and there is no way to send SMS for free. I'm sure there are millions of people would use this kind of service. Would it be possible to build a paid service for sending SMS worldwide? Is there any legal way? I know that there are some API services like Twilio but they are too expensive. What do you think?
Though I am unable to answer your question of whether a legal and profitable SMS system can be built, I'd like to point out a hidden answer in your statement — "after sometime they shut the service down, something happens. I don't know why"<p>Most of these "ugly websites" are fly by night operators. They are spammers looking for in-use phone numbers to build a database. The database then could be used to send bulk spam SMSes or could be sold to tele-marketers for a profit. So essentially these websites never make any profit from actually sending the SMS but instead scam the users to share their phone numbers.<p>Now you know why!
I was thinking about this a few months ago, but I couldn't find a way to make it affordable.<p>Showing banner ads doesn't seem to be enough, since the cost to send one SMS is greater than the profit from one banner. Perhaps that's why those sites had so many banners?