Oh Yeah? iPhone 4 = Single Core vs. Lumia 521 = Dual Core
Also 4" Display is much better than the 3,5" cause 3,5" is Definitly to small in my Eyes....
521 has 8 GB Storage + SD Card up to 64 GB also not as Bad...
Display is Maybe better from Resolution but now as i use a iPhone 4 as a iOS Test i can say u in the Sun Every Lumia Display can be read better!
Also the 620/521 will get more Updates as the Old iPhone 4 which has gut Updates but noch much Features (No Siri and Face Time over 3G for iPhone? REALLY APPLE?!)
And i really only Counted Technically site and not the Software/Use Problems iOS brings with it like u need iTunes or the Outdated UI...
I would Prefer a 620 much over a iPhone 4... But thats only my Opinion!