How to configure wifi on a proxy network

We are attempting to deploy iPhones to our enterprise but can seem to get the wifi setting to work. We can add the wifi network, the device sees it but when you choose the network in Seetings=>wifi, you get just a generic message "unable to join network.." on the device?

How are all the iPhone users at company's using their devices connecting thru the company wifi if that network uses a proxy to get out to the internet?

Or do you all just use the cellular network when wanting to browse the Internet? Also, how are you all getting to company data shares on your iOS devices if you can't get to the company wif network?

Any direction would be greatly appriciated.....