I have turned on imessage in my phones settings but it does not send imessage to all iphones in my phone book. Why does it send to some and not others, I have checked and they all have imessage turned on.
Aswell as needing an internet connection both devices need to be running iOS5. They also need to have imessage turned on withing settings>messages. If neither of the above is true then it wont work simple as.
Yes, if you are both connected to wi-fi or 3G it will send an iMessage by default as long as the iMessage is on. If for whatever reason either one of you are not connected to the internet it will then send it as a sms