Phone Extension Not Receiving Any External Calls...

[Lucas1]

nice to contact you.
Thanks for your continuously support for Yealink products.
I read your description, but also dont know why the issue occur.
could you please to check some question.
1,Do all extensions register same PBX server?
2,Can this extension receive internal call ?
3,please configurate this extension with other account ,check the issue if still exist?

In addtion,Please provide more issue data to us for analysis from phone.
1,trace
2,syslog(level 6)
3,config.bin
if you dont know how to get issue data ,please refer to http address
http://forum.yealink.com/forum/showthread.php?tid=1319.