asterisk users - Feb 2006 - ISDN busy line

I'm trying using Asterisk over an isdn line. I configured my Eicon Diva 
card by the hisax module and it works with the Asterisk's chan_modem 
(and chan_modem_i4l) driver. The problem is that I can receive calls (on 
/dev/ttyI0) but when I  make a  call I always have the line busy (on 
ttyI0 but even if I use an other device like ttyI1). This is a part of 
my consol output:

    -- Executing Dial("SIP/214-6621", "Modem/g0:338???????")
in new stack
    -- Called g0:338???????
    -- Modem[i4l]/ttyI0 is busy
    -- Hungup 'Modem[i4l]/ttyI0'
  == Everyone is busy/congested at this time (1:1/0/0)
    -- Executing Goto("SIP/214-6621", "s-BUSY|1") in new
stack
    -- Goto (macro-dialout-trunk,s-BUSY,1)

Using isdnlog command and watching results in /var/log/isdn.log I see 
that my call to 338??????? becomes a call to +39(my country 
prefix)38???????. Why does isdn miss a number (3)? Does someone think 
that the problem is in?
Thanks, Francesco.