AT&T has a significant problem handling unlocked google play devices that can cause your bandwidth to be capped around 2-3mbps. The problem is that the IMEI of the device isn’t automatically detected in the system as a phone that needs a “Dataplan for 4G Smartphones” and instead is marked as “Dataplan for Smartphones”.
You’ll need to call up AT&T support explain this problem to the rep. They will assign a dummy guid from a device that their system registers to your account as a workaround to assign the correct data plan.
After this, if you set your APN information correct, you can get much higher speeds. If you’re phone won’t work with these settings, it’s on the wrong data plan.
Name: AT&T US HSPA+ (This doesn’t matter)
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMS proxy: proxy.mobile.att.net
MMS port: 80
MCC: 310 (should be auto set to your country code)
MNC: 410 (should be auto set to your network code)
Authentication type: Not set
APN type: default,admin,fota,mms,supl,hipri
APN protocol: IPv4/IPv6
APN roaming protocol: IPv4/IPv6
Make sure you click the overflow button and hit save. These settings will also theoretically work for LTE Band 4 which the phone also supports but AT&T doesn’t have many towers supporting it yet, so it’s untested.
Enjoy your better speeds!