asterisk users - Dec 2006 - Problems with bridging data calls over Wildcard TE405P

Hi,

I recently installed an Asterisk server at a customer's here in
Germany, using a Wildcard TE405P - Ports 1 and 2 (group 1) are
connected to the phone system (Deutsche Telekom), whereas ports 3 and
4 (group 2) connect to the existing HiPath 3500 PABX.

Currently, the dialplan is doing nothing but routing calls through
(bridging) for the time being:
--
[inbound]
exten => _4048.,1,Dial(Zap/g2/${EXTEN})

[outbound]
exten => _0.,1,SetCIDNum(4048xxxx)
exten => _0.,n,Dial(Zap/g1/${EXTEN})
--
This works great for all voice calls inbound and outbound, also faxes
and modem calls are routed just fine.
Data calls from ISDN devices in both directions, however (like home
banking) are only connected, yet no data flows and after a couple
seconds the answering side hangs up.
At the console this looks like
--
    -- Executing SetCIDNum("Zap/119-1", "4048xxxx") in new
stack
    -- Executing Dial("Zap/119-1", "Zap/g1/0531590xxxx||tT")
in new stack
    -- Requested transfer capability: 0x08 - DIGITAL
    -- Called g1/0531590xxxx
    -- Zap/4-1 is ringing
    -- Zap/4-1 answered Zap/119-1
    -- Hungup 'Zap/4-1'
--

I tried to read up on everything regarding data calls, but only found
so much different, sometimes conflicting, info that I'm hoping
somebody here has some experience with that.

  Thanks

    Marc