iMessage appears in the new iOS 5 software due to land next week.
It's an intelligent messaging app that handles IM via wifi or 3G complete with all of the IM bells and whistles like read receipts etc.
It also handles conventional SMS and will switch to this if you are a) not messaging a fellow iOS 5 imessage user or b) don't have wifi or 3G reception in your area but do have regular phone reception
One of the great features of this app is that it work across iPad and iPhone. Therefore when someone messages me from their iPhone it will deliver to both my iPhone 4 and iPad 2! Sweet eh! I can also have a conversation from my phone and continue it at home later on my iPad.
We will have to see how it pans out when it's launched but on paper at least it sounds ace.
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I am here:
http://maps.google.com/maps?ll=51.522676,-0.708449