The signalling of the FXO interface is "FXSKS" in the Zap configuration. And I have only one FXO interface and only a "Catch-all" inbound route for the FXO. I also associated DID with the trunk ( Because the FreePBX requires configuration like that!).
I read the following document in voip-info.org:
"immediate: Normally (i.e. with immediate set to 'no', the default), when you lift an FXS handset, the Zaptel driver provides you a dialtone and listens for digits that you dial, passing them on to Asterisk. Asterisk waits until the number you've dialled matches an extension, and then begins executing the first command on the matching extension. If you set immediate=yes, then Asterisk will instruct the Zaptel driver to not generate a dialtone when you lift a handset, instead passing control immediately to Asterisk. Asterisk will start executing the commands for this channel's "s" extension. This is sometimes referred to as "batphone mode". Default: no.
Will changing "immediate=yes" resolve my problem ? Are you sure? I use my asterisk system in a productive environment. I had interrupted the system many times and had been complained a lot. I am afraid to interrupt it again without any result.
The signalling I was referring to was the provider's signalling, YOUR signalling must match their's just as danardf says, that includes ringing, dialtone disconnect etc. Check/set you country locale
immediate=yes WILL change the behavior of the trunk but it might prevent outbound calls (deprnding on the telco provisioning) so test at night also
(thios requires boath a asterisk restart and a zaptel/dadhdi restart. (do at night)