I have an application that communicates via SSL, however, Port 443 is already in use by an IIS instance on that same server. Can I use another port other than 443 for SSL communication?
SSL is in no way tied to a single port value; in fact, as a protocol, it can be used over any transport medium, as long as that medium provides a bidirectional stream for arbitrary bytes.
In a Web context, you can use any port other than 443, provided that you specify it in the URL:
Note that there are some networks (especially some free WiFi access points) that don't allow traffic over other ports than 443 or 80; which means that using a port other than 443, though perfectly standard and supported, may imply some practical usage restrictions.
On Apache you can do this on the same port: http://www.digicert.com/ssl-support/apache-multiple-ssl-certificates-using-sni.htm
You can use (nearly) every port, which is not used, for SSL communication. The question is: Did you mean that someone enters
https://... and your service is not on port 443? Than it is not directly possible. Modern browsers use the prefix
https:// to connect to
serveraddress:443 (if no port is present). Similar to
http:// which connects to