As you may already know, a lot of SIP phones needs to be programmed via a web interface and web interfaces usually use port 80.  Well this tool 'SIP Flanker' found here can search a range of IP addresses to see if port 5060 is present i.e. a SIP device, then probe port 80 to gain access to the web service on the SIP device.  Obviously this is a neat trick but maybe you want to try it out to see what damage can be caused.