Sync with Exchange via GPRS and USB

[BlueDun]

Hi,

after trying for hours I really need help:

ENVIRONMENT:
ELF (Htc Touch)
Laptop with Vista and Mobile Device Center 6.1
Office/Outlook 2007
Server 2003

WHAT I WANT:
Sync with our company exchange server both via GPRS (when I'm traveling) and USB (when I'm in the office)

Sync via GPRS works flawless. I configured the exchange settings manually. Synchronization of mails, contacts, and calendar works fine.

Problems start when I connect the device to my PC via USB.
The PC is in this case connected to our company LAN. After I plug in USB mobile device center connects and the synchronization starts. Problem is that it never ends. My device shows "waiting for network" and nothing happens thereafter. In the mobile device center error messages begin to pile up (saying that sync failed).
Aparently the device cannot connect to the exchange server via USB and the PC as gateway (at least, that's what I conclude from the messages). I've been playing with all settings I found but I'm stuck with the same problem.

There must be a way to do this! After all I had that in my old company (Windows xp and Windows Mobile 5), although i had to manually chose which connection I wanted to use.

PLZ Help !!!

Thanks
BlueDun

[BlueDun]

I found something!

Our exchange server has for internal (LAN) and external (internet) access different adresses. No wonder that it could not connect.

But there's the next problem: How do I configure so that I can chose the server depending on the connection I'm using? Of course, I could go to the exchange settings and change them every time I want to access but there must be an easier was that allows me to preconfigure two profiles for the same outlook mobile account.

Ideas please ...

Thanks