Why is it that sometimes when I send a text to another iPhone I get billed as text time?

I normally send text to other iphones using the imessage in color blue... sometimes all of the sudden appears in green like sent as text. Any help?
Thanks

as stated in this link http://support.apple.com/kb/HT3529 when imessage is unavailable it will send it as a SMS.
to troubleshoot look here http://support.apple.com/kb/ts2755

Similar Messages

Maybe you are looking for