I am not sure how it is for IBM J9, but for the Motorola IDEN phones the code looks like that:
String url = "comm:com0;baudrate=19200;databits=8;"+
"stopbits=1;parity=n;flowcontrol=h";
CommConnection cc = (CommConnection)Connector.open(url);
I think you won't need to specify the params after the baud rate, since those are the defaults.
Hope it helps,
Yuri