Currently Being ModeratedOct 14, 2011 3:26 PM (in response to grayalne)
SMS is set to on and so is MMS
Currently Being ModeratedOct 19, 2011 2:12 PM (in response to grayalne)
I'm having this problem too; if an iMessage isn't delivered it will be sit there for a good few minutes before apple decides to send as a text message instead.
However I just discovered a handy part solution; if you press and hold the undelivered iMessage an option pops up to send as a text message.