Click on the 4s discussion for this forum and you will see i am having the same question and even more regarding this blue and green msg stuff.
Different factors can cause the iMessage to switch from iMessage to regular sms message. If the server is down it can happen. If for some reason one of the iPhone users device is having trouble connecting to the server then messages sent to/from their device will switch to sms. If either user has disabled iMessage it will happen. If the 1st 2 occur a quick "fix" would be to restart the device. I have had this happen only once since iMessage came out...and it didn't happen on my device...it happened on my mother's. She was at someone's house and our messages to each other came as sms instead of iMessage. When she came home I restarted her device and it was back to normal. Not sure why the issue occurred, but it was easily fixed. With iMessage being relatively new there are bound to be various connection issues from time to time, but I'm not aware of too many people that have constant issues with it switching on them. If you think it's a much bigger issue you can always report the problem to Apple...if the issue is deemed to be widespread they are more likely to address the issue with a iOS update....just can't predict how quickly it would be done.
Me too. Off and on green and blue. Blur is good imessageing then turns green which means text. I
Very carefully avoiding that by haveing given that I have unchecked SMS for sent. My husband keeps imessageing on and SMS off. Usually it let's me send even if his phones off. I was charged a lot once. I would understand if it wasent To another iPhone. I don't like paying for things that should be free. Now we have a vzw text block that was suggested by vzw buy still I shouldn't have to do that. Vzw didn't even believe me when I had the setting to off and even after apple told them they didn't believe it.