Pushme.to is a free instant messenger for the iPod Touch, iPad, and iPhone. It is meant to be an alternative to SMS when a user is running low or is out of monthly SMS.
This is a great application for anyone looking to save on message fees. Much like BBM to blackberry users, this is exclusive to Apple mobile users. However, people can link their pushme.to profiles online or onto their facebook accounts so they can message from or to a computer via an internet browser. Attachments can be sent using pushme.to, and the interface has drastically improved since being released to the Apple store.
One main problem I found with this app is that it claims to be an SMS alternative. However, you can only message Apple mobile users. There are other applications that allow messaging to other mobile devices like Textfree. This is more of an AIM type of application.
THE BOTTOM LINE:
The quality of the application is something to be looked at. If you are friends with plenty of iPhone users or want another way to message people on a wifi-enabled Apple device, I would recommend using this product. If you do not and just need an SMS alternative, I would recommend finding an app that uses a secondary SMS phone number and not a social network profile.