A while ago, I had tried out a service called Pinger, which allows you to send voice messages to anyone within the U.S.. You basically dial a number, say or dial who you want to send a voice message to, give it a voice tag, and that person gets a text message to call a specific number to receive their voice message.

Now Pinger works in 20 different countries for the same price of free. That means, you can call one of Pinger's local numbers in the U.S. and leave a voice message for a buddy in another country. For free.

While I'm sure they are making something on the inbound calls, the question is, is this a sustainable business model? Outbound SMS isn't free, but it's relatively cheap. I'm sure it costs something to develop and maintain the infrastructure bits as well. What do you think?