I would strongly recommend you to install WhatsApp Messenger on your mobile devices! This is free, multiplatform (android, iOS, symbian, windows, blackberry) application which allows you to text for free. It uses only your data transfer (free Wi-Fi or cellular data). This is much more than communicator like palringo, skype or gg because it works just like simple text messages – once you receive message you are notified and what is more you don’t have to keep it running!
The reason I write about it, is that I want more my friends to use it so I can text with them for free – install it and find me with my mobile number;) You can download it from AppStore, Android Market or look here: http://www.whatsapp.com/
Here you have couple of screenshots which I’ve just made on my phone: