I sold my iPhone 4 on eBay a few weeks ago, so obviously, I have to go back to my old Blackberry. I didn't restore the iPhone immediately, so while waiting for someone to buy it, I was using the phone as an iPod touch. I turned on wi-fi and surprise, surprise! I received a text message from my fellow iPhone user and I can reply back as well. On my iPhone screen, it showed that the message is sent/received an iMessage (blue bubble). I can even see the "delivered" sign or when my friend was typing a reply. But on my friend's iPhone, it showed message was sent/received as regular text messages (green screen). Meanwhile, I don't receive the text message on my BB even though it's fully functional. I have to turn-off the wifi on the iPhone and then I'll receive a text message on my BB. It only happens if the person texting you is using an iPhone/iPad/iPod touch user with iOS 5 as well. Whatsapp works too with the SIM card removed.