For iPhone, there are several chat software comparable to the famous Blackberry messenger, very popular with its users. It is indeed an economical alternative to SMS to stay in contact with his tribe.
There was talk of Ping in this note, to use, it is convenient with the necessary support and push works quite well. But ... he is paying now for our ticket.
So for those who want a free solution with features similar Buzzme here!. The use is very simple, you choose a nickname and you can start sending messages to your contacts buzzme. For bringing a feature to send a message offering keur load and install the software. The push works well, you can associate custom ringtones to your contacts to recognize by ear ;-).
I put my hand on Whatsapp when it was free and the best three I have tried.
It automatically detects contacts with the application, no need to add them individually!
But it is true that only one application for free could actually claim has become a standard.