how do i enable delivery report for text messages

Delivery (and read) confirmations are available for iMessages (blue). Delivery is always on and should be visible under the most recent sent text. To see delivery status and time stamp for older texts, slide them slightly to the left.

Delivery and read receipts are not available for standard (green) text messages.

Note that when you enable read receipts on your device, that merely sends others a read receipt when you read the messages they send to you. To receive read receipts from others, they would have to enable read receipts on their devices. Read receipts are always under the control of the recipient, not the sender.

OPKhadka wrote:

This was infact a feature of a most basic phone available in the market. Is it not ridiculous to see this lacking in a premium phone ?

It's actually not all that common on phones in the U.S. However, you can certainly submit feedback to Apple suggesting they add the feature:

http://www.apple.com/feedback

One thing to add to Rysz's post is that "read" status is entirely under the control of the person your sending the message to. They have to turn that feature on.