5 telephone 1 base - BIG HELP BRO

good evening everybody, and good weekend; I need yours help, in my NEW office I have to take care about asterisk system and sometimes I have to place 4 telephones A540 for 1 base and 1 ethernet cable so. My problem is the most part of telephones don’t have an external number so they work with the master number from outside, and I don’t why the telephones with no external number sometimes they can’t call even other number inside the office. I mean they resul busy but they don’t need to use the external number to call another phone inside the office. ONLY the telephones with external number associated always work, WHY ???

WHY SOMETIMES THE TELEPHONES NUMBER 3 4 5 ASSOCIATED WITH A UNIQUE BASE RESULT BUSY ? ( THEY DON’T HAVE EXTERNAL NUMBER) AND WHY THE PHONES WITH EXTERNAL NUMBER WORK EVERYTIMES ?

It will only be possible to attempt to answer those questions in the context of the specific configuration of your system.

what do u need? extensiiion.conf ?