[channels]
        context = default
        switchtype = national
        usecallerid = yes
        echocancel = yes
        echocancelwhenbridged = yes
        ;add the is option if you are problems with DTMF detection
        relaxdtmf = yes
        rxgain = 0.0
        txgain = 0.0
        signalling = fxo_ks
        group = 1
        channel => 1-4

[channels] 
         context = from-pstn
         switchtype = national
         usecallerid = yes        
         echocancel = yes
         echocancelwhenbridged = yes
         ;add the is option if you are problems with DTMF detection
         relaxdtmf = yes    
         rxgain = 0.0
         txgain = 0.0
         signalling = pri_cpe
         group = 1
         channel => 25-34




zaptel.conf


# ports for analog card
fxoks = 1-4

#ports and span definitions for T1 card
#note: span number is 2
span = 2,1,0,esf,b8zs
bchan = 25-34
dchan = 48



/var/log/asterisk/messages
Sep  4 11:28:36 NOTICE[5573] cdr.c: CDR simple logging enabled.
Sep  4 11:28:36 WARNING[5573] pbx.c: Unable to register extension '2718', priority 500 in 'default', already in use
Sep  4 11:28:36 WARNING[5573] pbx_config.c: Unable to register extension at line 606