Cell C have quietly opened up LTE for iPhone 5 users. We received a tip early on 11 May that there was a carrier update available which would enable LTE on the iPhone 5. Upon further investigation it seems that Cell C had even informed Apple about the change as the Apple website now shows that Cell C supports LTE in South Africa, 10 days ago this page didn't have Cell C listed.
You can enable LTE on your Cell C iPhone 5 by going to Settings, General, Cellular, and there should be an Enable LTE option there. If the option is not available go to Settings, General, Cellular, Cellular Data Network and at the bottom Reset Settings. It will let you know that there are new network carrier settings, this will update your settings to enable LTE.