After reading this board, I tried and succeeded with the following:
#setserial /dev/ttyS1 irq 0
So I take the eth cable out, put the modem in, then execute the above line. And it works flawlessly.
And no modifying /etc/pcmcia/config.opts does not fix the problem... I will setup a script similar to:
setserial /dev/ttyS1 irq 0
To get the PPP connection working