I have an iPhone 4, sometimes I get the green sms bubble and sometimes an iMessage bubble. At times it states sent as text message and sometimes it doesn't. When it doesn't does that mean the message has been sent out?
When the bubble is blue, the message is send as an iMessage. If it turn green, it is send as a regular SMS.
The iMessages have a build in delivery report and is will tell you tings like 'delivered' or 'read' when the message gets delivered/read.
However, a regular SMS doesn't provide these options, so you'll have to install some 3th party software to get this kind of feedback. So you have to trust your provider to make sure your message gets delivered.
If you have jailbroken your device, there is an SMS Delivery Report repository in Cydia.
If you don't like your iMessages to be sent as a regular text, you can simply turn this feature off in the Settings < Messages < Send As SMS
When the iPhone doesn’t show the “Sent as Text Message,” and the bubble is blue in colour, the message was sent as iMessage. That means the message has definitely been sent, because iMessage has the ability to report an error with the help of a red exclamation mark beside the message.