How to select 2G as data network on iOS 8?

It is stated on the iOS 8.1 release notes that users can now select 2G, 3G or 4G LTE as their data network.

I've since updated to iOS 8.1 but I could not find where the option is to select 2G data network.

Where can I find this setting option?

It can be found in Settings > Cellular > Voice & Data where in the option is available to select between 2G,3G and LTE.

If the voice option is not available for your iPhone. Please call and check with your respective service/carrier provider.

It's been noted that some of the carrier update for the iOS 8 has removed the "Voice & Data" option because Apple let the carriers to update the cellular settings. It's only a matter of reverting back the update from the service/carrier providers.