ussnorway: We've currently basically have the same phone. The 521 is the T-Mobile version of the 520. I think the only difference between the two, if I remember correctly is tge 521 supposedly can get low level 4G (no LTE) and the 520 can't. I don't understand one thing Microsoft is doing with the newer Lumia's. Every Lumia under Microsoft, only has 4GBs. of internal storage. Considering our older Nokia Lumia's have 8GBs. on board. Granted, here's what they want you to think : The newer 2014-15 model's can use a 128GB microSD card. I'm almost positive, any Lumia that's running Windows Phone 8.1 can use the 128GB. microSD cards, too. That's a feature in Windows Phone 8.1 that wasn't in WP 8.