@Adam Rosenthal Our engineer said the the coreboard is a 15 digit IMEI, do you mean that you connect the AT&T SIM card but it could not recognize your SIM?
As to the sound quality, we have a new firmware to get it improved and it's about to be released in May. We will let you know then.
@Support Dasaita
I have already been through this. Count the digits on my IMEI. don't worry about the ATT card. It doesn't work anyway. My unt does not have enough digits in the IMEI
@Adam Rosenthal Please kindly go to Settings > System > Factory reset the head unit to check if the page will change or not.
In the mean while, down the zlink(v5.4.40):https://www.dropbox.com/scl/fi/jrya42umgerwzjo8atxtx/zlink5-hengchangtong-release-v5.4.40-34f63965f_jg.apk?rlkey=20lv6wzz6ci0qgchc7fvb7pb2&dl=0
Go to APKinstaller to update the zlink and verify if the microphone quality could be improved or not.