Differences between the two Nexus 5 models, D820 and D821
The D820 version of the Nexus 5 is designed for North America and will connect to 2G, 3G or LTE on AT&T, T-Mobile and Sprint. The D821 version of the Nexus 5 is set up to work with the rest of the world. European users should have no problem with a 2G, 3G or LTE connection. But some of the Asian carriers that use different networks could pose a problem. For example, China Mobile uses a proprietary 3G pipeline that has kept the Apple iPhone off the roster of the world's largest carrier.