In South Africa it is becoming more difficult to send free SMS's this way. Vodacom gives you 20 a day and MTN 5 - but you have to jump through loops and register. Then also you cannot send from Vodacom to MTN and vice versa. In other words, it is limited to MTN to MTN and Vodacom to Vodacom.
This service works worldwide and seems to overcome the local barriers.
The fact that I am considered an adult is both terrifying and hillarious