Can two different phone numbers be used to receive voice and text on one iPhone?
The short answer appears to be no - regarding an iOS 6 device. It certainly isn't possible without jailbreaking. Also iPhone's Phone.app and Messages are clearly designed for a 1 phone number type setup.

However, there may be some "hacks" that may work well for you. If I were you, I would look into Google Voice. It certainly isn't ideal, but may be the best you can get. What you can do is have things forwarded to your regular phone number. 

Check out http://www.google.com/voice/.

I believe you could work it so that you port one number into Google Voice, and then have your main/regular number on your iPhone in a standard way. When you get a call from your alternate phone number I believe it will forward it to your normal number and allow you to take the call normally. You can get the Google Voice app to text and call from your alternate phone number. The catch with that is that you will need data service - not just voice signal.