I restored a backup on a new freepbx with less extensions than the older one.
At first only worked the phones that was on the old pbx.
After looking what happened I saw that freepbx on backup restore don't create de db entries:
/AMPUSER/100/cidname : xxxxx
/AMPUSER/100/cidnum : 100
/AMPUSER/100/device : 100
/AMPUSER/100/language :
/AMPUSER/100/noanswer :
/AMPUSER/100/outboundcid :
/AMPUSER/100/password :
/AMPUSER/100/recording : out=Never|in=Never
/AMPUSER/100/ringtimer : 0
/AMPUSER/100/voicemail : default
To create it i had to go for each extension and click on submit button.
As I saw freepbx creates db entries when you click submit button and not when apply change button is clicked. When you restore a backup you must restore de db without submit each extensions.