This statement is taken verbatim from the mtnsms web site:

mtnsms ends free service on march 5th:

over 7 million people from 140 countries joined our community & connected the world.

people proposed & broke up on our service. we were told we saved lives.
during the past three years, we sent over 1 billion messages.

we also pioneered net2cell2net sms with our twist (two-way instant short text) engine.
as costs increased, we introduced advertising, but it was only a partial answer.
now another set of charges from 3rd party networks has hit our service.
the time for the experiment is over.

The site will be closed to International networks but users will still be able to send messages to MTN subscribers in South Africa.

2 our loyal community
7 million thanks for making mtnsms the most popular sms site on the world wide web.

2 our partner network mtn
1 billion thanks for carrying all the costs in this great 3 year experiment.

we will b back
within the next month we hope to evolve into an even more exciting sms experience.
peace 2u all.
airborn.