There are a couple of iPhone apps that I started using recently. One is WhatsApp which is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS.
A cool thing is that it is available for iPhone, BlackBerry, Android and Nokia.
In addition to basic messaging iPhone, Android and BlackBerry WhatsApp Messenger users can send each other unlimited images, video and audio media messages and even a map with your current location.
The nice thing they just add with 2.6.x version is Group Chats. It took me a while to find how they worked. Go to Chats and pull down. A menu appears on top with broadcast message and group chat. Groups could contain 5 people at this point, but it is great.
For this you could also use Beluga which is basically for group texting plus a cool map to see where all your friends from a group are. The cool thing about Beluga is that you can create groups easily: a group for the ski outing, then see where everybody is and chat and send photos for free. WhatsApp groups has not the map with everybody but the rest you can do too, and more! share voice messages, videos, …
The third app I wanted to talk about is Viber. Viber is an iPhone application so far, but coming soon on Android and Blackberry. It lets you make free phone calls to other iPhone users that have Viber installed.
When you use Viber, your phone calls to any other Viber user are free, and the sound quality is much better than a regular call. You can call any Viber user, anywhere in the world, for free.
You could argue that for this you have skype or other messenger, but I was surprised to see how many people of my contact list (it scans it) had it. Also it just runs on the back, it uses push so you don’t drain battery.