There 2 IP phone cannot working, the 1st cannot dial and answer and the 2nd cannot answer call.

I face issue at customer side for two ip phones " the 1st cannot dial  and answer and the 2nd cannot recevice call. "

for the first IP phone :

I check the registration of this IP phone , i found it faulty , i cehck the configuration it was OK , the issue was with phyiscal network connection so we changed the ethernet cable , then IP phone working fine .

For the second IP phone :

the customer enable DND function, so it cannot answer call. so i disable DID feature .