Occassionally, after a connection is established and closed again, Windows “loses” the modem. It is still in the device manager available, but in the next connection attempt, Windows uses another device in the dail-up connection instead. I examined this behaviour and found out, that deactivation and re-activation the modem in the device manager preserves from this strange behaviour.
Any explanations on this are highly appreciated
TS 
No suggestions at all??
Hi Troubleshooter,
I would try another GSM modem. I mean from another manufacturer. If the problem still exists, it’s a windows problem 
Best Regards,
Jan
I have a customer who is experiencing the same issue - could it be caused if they don’t have flow control on the RS-232 link to the modem??
Quite possibly!
If you don’t have flow control, you will lose data sooner or later - and, thereafter, you’re into Undefined Behaviour territory… 