ISDN Data Dial in

I have a customer that wants to dial into an ISDN modem with Windows Mobile 5 terminal. When using analogue modems he has no problem with data com but his ISDN does not recognize the dial in.
With a different terminal that has integrated Siemens modem he uses ATDI(n) or I(n) without problems.
Since I do not have a manual for AT commands maybe I can get some help here?

What, exactly, happens?

Can you get any diagnostics from the ISDN thing?

Does the documentation for the ISDN thing give any specific guidance? Have you asked their support?

Are you sure that the SIM supports it?

Have you checked the clearing cause from the Wavecom unit?

Are they custom Siemens extensions?
What, exactly, do they do…?

Ask your distributor, or download it from the ‘Products’ section! 8)