How can I send message as Text Message on purpose? I have noticed that iMessages usually fail when outside a reliable data network area. Only after iOS attempts to deliver the message and fails does it offer to send it as a text message. Often the failure takes some time, and is not brought to my attention immediately. When circumstances are such that I reasonably suspect that iMessage will fail, I would like to skip the failure and send an SMS immediately. 

How can I opt to send an SMS message instead of an iMessage without first attempting to send an iMessage?
There is currently no way to switch to Text Message by default when iMessage you know is going to fail. 

1) When you know that your iMessage is not gonna go then try this:


Type iMessage and send it. It will get stuck with Top bar showing "Sending..."
Long press the iMessage text that is not going.
A menu will appear where you can choose "Send as text message"


2) Now if you want to send Text Message intentionally by passing iMessage (consider scenario when you know recipient is not on cellular data or wifi) you can do the following:
- Disable your Wifi
- Disable Cellular data ( Go to Settings -> Select "Cellular" -> disable "Cellular Data"
- Type iMessage and send it. It will get stuck with Top bar showing "Sending..."
- Long press the iMessage text that is not going.
- A menu will appear where you can choose "Send as text message"

Hope that helps!

Screenshots attached:Updating after fsb's comment below. "Send as text message" is not disabled in iOS 10.2.1 (latest as of 02/21/2017)