Handytone HT-488 outgoing PSTN problem

I have this ATA with Asterisk and I managed to get incoming calls working. However, I found no way to coax the box to make an outgoing call over PSTN. Here are some relevant setup details:

a) Hadytone

  • “Forward to VOIP” is set at 901
  • “Route to PSTN” is blank (I tried it with non blank values)
  • “PSTN acess” is at the default of *00

b) sip.conf

port = 5060
bindaddr =
context = default
srvlookup = yes

callerid=Konsultex SP

c) extensions.conf

exten => 901,1,Background(pls-wait-connect-call)
exten => 901,2,Goto(pbx-in,pbx,1)
exten => 902,1,SayDigits(*00${PSTN})
exten => 902,2,Dial(SIP/ht488-1-fxo1,D(*00${PSTN}))
exten => 902,3,Congestion( )
exten => 902,102,Congestion( )

I place calls prefixing a “5” to the PSTN number, like this:

exten => _5.,1,Set(PSTN=${EXTEN:1})
exten => _5.,2,Goto(ht488-1-fxo1,902,1)

The FXO port is connected to the PSTN phne line and the FXS port is connected to our conventional PBX (to a trunk so that our receptionist answers the call as before) which we are using mostly as a way to keep the traditional phones with Asterisk. Incoming calls on that PSTN line are transfered to extension 901 and handled by the Asterisk logic with the Goto() statement. This works fine. But if I dial a number to go out on the FXO port (for example 5 3819 1765) I can hear the correct digits being passed by Asterisk to the HT-488 but then the HT-488 does not seem to dial out.

Any clues that could solve this problem?