Sim can not be installed ower kopete, but kopete can be installed ower sim.
I've looked throw the kopete package, and found how kopete manage this situation. I think sim shoul do the same... See attached file ;-)
diff -u -r sim-0.9.3.etalon/debian/control sim-0.9.3/debian/control --- sim-0.9.3.etalon/debian/control 2005-12-02 13:01:39.000000000 +0300 +++ sim-0.9.3/debian/control 2005-12-02 13:05:26.000000000 +0300 @@ -12,6 +12,7 @@ Package: sim Architecture: any Depends: ${shlibs:Depends} +Replaces: kopete Description: Simple Instant Messenger SIM is a open-source ICQ client, using QT with enhanced features. Special support for KDE3.