I seem to be having a problem with iMessage on my IP4. It will work as intended when I'm on wi-fi, but when I'm on 3G it will try to send as an iMessage, and not a standard text. As I understand it is meant to realise when it's on wi-fi or 3G and use either text or IM? I can get around it by waiting for the IM to fail and then force it to send as a text, but I usually forget this and don't realise it hasn't sent. Any ideas?