Discovered ping! (http://www.pingmessaging.com/Ping!/Ping!.html) yesterday; it seems quite a cool little app for the iphone – namely (once you know another iphone user has it and their username) it allows you to sms them for free. In non-scientific tests it seems as quick, if not quicker, than our carriers SMS.
I can’t see why (when ping! registers with the server) it can’t disclose your mobile number, and allow that to be your username, it would be so much more obvious than e.g. david-goodwin.
It has pretty much no integration with any of the rest of the iphone – e.g. address book etc, and if you delete a thread you seem to need to remember someone’s ID to message them again.
Then again, it’s free to install, messaging is free, and O2 only give me 500 free texts a month.. which get easily gobbled up when you send a message longer than 10-20 words.
ping! would also be free to text people who are abroad; luckily for them I don’t know anyone abroad with an iphone who I’d want to text much (if any).