Tagg is a free web & mobile based mass messaging platform that you can use for any of your purposes. This could be for (seemingly) noble causes like group SMS, micro-blogging etc, or for less noble ones like spamming users with unsolicited SMS (by users, not by Tagg).
The way it works is fairly simple. You can start a group (called Taggivity) which others can subscribe to. You can send out updates that will get forwarded to all the subscribers. This can be done from the web interface or from the mobile usings SMS. Their revenue model is based on advertising - text/banners ad on the website and a short ad that is appended to SMS’s being sent out.
Group SMS is actually a valuable service. I can imagine lots of people wanting to use this - organisations, schools, teachers, salesmen etc. The ability to send our free SMS to all subscribers (who could be students, employees, friends, family members etc) is fairly useful. Specially when its free. And SMS is a proven winner…. no GPRS, EDGE, 3G hangovers there.
SMSgupshup is a similar service and I believe, it has a fair bit of traction as well. So how is Tagg any different from SMSgupshup? Well the Tagg team insists that they are more focused on user experience- as a result they have a normal number 9980199801 as opposed to a shortcode, which also means its cheaper for user to post through their service. Not entirely convincing, I would say!
The web application could do with better layout & design, specially on the landing page for an individual group.