context default {
    include office_extensions;
}

context office_extensions {
    include standard_extensions;
    "411" => directory;
    "456" => conference;
    "519" => bridge;
}

context standard_extensions {
    "_1XX" => standard_extensions;
}

context long_distance {
    include local;
    "_1NXXNXXXXXX", "_NXXNXXXXXX" => long_distance;
}

context local {
    include default;
    include parkedcalls;
    "_NXXXXXX" => local_call;
    "_1800NXXXXXX",
    "_1888NXXXXXX",
    "_1877NXXXXXX",
    "_1866NXXXXXX" => tollfree_call;
}

..... Above is dial plan configuration (which is a set of contexts)    .....
..... and, below is dial plan execution (which is a set of extensions) .....

extension long_distance
    dialout(extension);

extension local_call
    dialout(extension);

extension tollfree_call
    dialout(extension);

void dialout( string extension, int timeout ) {
    // er this is where i stopped today....
    SetCallerID(1234567890);
    SetCIDName(Big Company);
}

extension standard_extensions {
    string status;

    status = Dial( "SIP/exten".extension, 20, "t" );
    switch status {
        case "ANSWER" {
        }
        case "BUSY" {
            status = Voicemail("b", extension );
        }
        default {
            status = Voicemail("u", extension );
        }
    }

    // Status gotten from voicmail
    if status == "a"
        VoicemailMain( extension );

    // Go to the default context so that you can still dial something else.
    goto_context( default );
}

extension directory
    Directory(default);

extension conference
    Meetme(4569);

extension bridge
    Dial(IAX2/aouaoeu@asdfasdf/100);