modem error 633:modem already in use

With my dell laptop(OS is Vista),I use my modem driver dial and
download files from Internet.
Then the laptop sleeps (stand by),After a moment ,the laptop wake and I dial again.
There is a 633 error:modem already in use.
It seems that some error happens,
But if I use hypertrm and open the com port of the modem,it is OK.

The Dial-up does not hang-up until Vista wake and the modem driver will
unload and load when Vista wake ,
I guess maybe one application use the modem and before it release the modem,
the modem unload and load,so the application can not use the modem again ?
And how can I fix it?

And the modem driver is a usb modem driver for a moblie phone.