It isn't actually a fourth phone. I borrowed the Lumia 520 from work when the Xperia started to flake out on me. The problem with dual-sim phones is pretty enduring, there are few any Westerner would want. They're oriented to the irrational Indian and Chinese wireless markets where many need multiple sim cards. There was supposed to be a dual-sim Lumia 630 with North American 3G but it doesn't appear to have materialized.