Want a cheap gateway to the world of Windows Phone? In the US, it won't get much cheaper than AT&T's new version of the Lumia 520. Nokia's starter device will cost just $100 contract-free when it hits AT&T's GoPhone prepaid service on July 26th -- that's $50 less than T-Mobile's already inexpensive Lumia 521. There won't be LTE support or other frills, but we suspect that many customers won't mind at this price.