1. I never had 4G capability until this phone (coming from SG2)
Since I had a standard size SIM, I had to go get an LTE enabled microSIM to fit this phone at the AT&T store.
2. I registered my IMEI with AT&T
DO NOT register your OF7a with AT&T, since it's an unrecognized phone, it will default to pretty much trash and you'll lose any chance of 4G until you do what I had to do.
What I did was take my wife's phone (LTE enabled GSIII) and put my microSIM inside. Powered the phone on, let it recognize my SIM.. and then I contacted ATT via Messenger on their site. Told them that I was using my wife's phone and that I didn't have LTE on it, but she did whenever she used it.. Gave them the IMEI number for the GSIII and after he made his updates in his system, he had my power off my phone for 90 secs. After I powered the phone back on, and just like that, I had LTE on the SG3 with my SIM.. thanked the tech and popped my SIM back into the OF7a and viola! All good.. Now that I have confirmed 4G LTE on the OF7a, I've been playing around with different APNs... so far my favorite is as follows:
down: 30-45 up: 16+
Name: Anything you want, I called it OPPO PTA
Proxy: not set
Port: not set
Username: not set
Password: not set
Server: not set
MMS proxy: proxy.mobile.net
MMS port: 80
Authentication type: not set
APN type: default,sup,mms
APN roaming protocol: IPv4
Hope this helps.
Not sure if I can post other forum links where I figured out where I went wrong, but it's the Oppo Forums (No ATT LTE with 7a US Edition)