In order to activate NTC 3G in prepaid and postpaid sim, you need to subscribe NTC 3G first.
How to subscribe NTC 3G in old prepaid and postpaid sim card
Step I: Go to your message box
Step II: Open new message and type 3G
Step III: Send the message to 1400
3G will be activated in your sim by 5 pm of next working day.
(No charge will be applied for sending this message)
3G is already activated by default in case of new sim card.
How to change 2G Sim to 3G Sim
The process for subscribing 3G in 2G sim card is same. All you need to do is to go to message box, type 3G and send it to 1400.

NTC 3G Net setting for Prepaid and Postpaid
[How to Activate] NTC 3G Net setting in android and iphone set
If you are using NTC sim card, the process of activating 3G is same for both prepaid as well as postpaid sim cards. Ask for automatic GPRS configuration in your set as below:
Step I: Go to your message box
Step II: Type gprs if you do not know the model of your set.
Type gprs for Nokia, LG, Motorola and Indian mobile sets like Colors
Type sagprs for Samsung set
Type segprs for Sony Ericson
Type chgprs for Chinese sets
Step III: Send the message to 1404
This is how you can activate 3G for NTC Android sets.