[stephen122333]

I have an iphone6 and an ipad2 both have io8.1 installed, both are on the same wifi network, and both logged into the same icloud account.

I have gone into
settings
messages,
but I do not see any option on how to turn on this feature.

Any hints or tips, many thanks

[Stig]

Google says:

Make sure your Mac, iPad and iPhone are all connected to the same Wi-Fi connection.
Make sure all of the devices are logged-in to the same iCloud account. You don’t want to be receiving your father’s phone calls, do you?
Starting with your iPhone first – and this is important, because I did it backwards and messed everything up – open Settings > Messages and tap “Text Message Forwarding.”
Choose the devices on your home network that you’d like to receive SMS messages on – in this case, I chose my MacBook Air and my iPad.
You should receive a code on your iMac and iPad.
Enter that code into the prompt on your iPhone.