Extraido del FAQ de JCA:
http://java.sun.com/products/javacomm/CommAPI_FAQ.txt
Q: Can I use the Java communications API in applets?
A: Yes in signed applets, but no in unsigned applets (most cases). Since we
do not allow unsigned applets access to any communications port under the
JDK1.1 security model, you can not use the Java communications API with
unsigned applets. We do plan to be compliant to JDK1.2 security model in
later releases, which might allow trusted applet access to ports.