Dial conversion [SOLVED]

I have a problem defining in extensions.conf what I want to happen:
If I dial on my phone: 0612345678 I would like to rewrite that in order to get it in the right format before I send it to my SIP provider, but I can’t get it to work. Can someone tell me what I do wrong here:

[voip-out]
exten => _06.,1,Dial(SIP/00316.@voip-2,30,tr)
exten => _06.,2,Congestion

thanks, Jos

,Dial(SIP/0031${EXTEN:1}@voip-2,30,tr)

Aha; so the EXTEN:1 does force the first character to be stripped and the 0031$ adds the number to the remaining 6, right?

thanks for sharing.