Have you tried hangouts.google.com? It's possibly still blocked, depending on your employer, but if not, it's just a hangouts webUI that also allows calls.
Hangouts actually works at the moment, but work could change that at anytime, so making it a key piece of my workflow is unwise. I get your point though.
Employer blocks Gmail (and other sites) via the corporate firewall. They are not paying for Google Apps (at least not for me). Get a job at any large enterprise and you'll experience some restrictions you wouldn't find at a smaller company.
My employer also blocks some Google services. For example, I can't access Gmail. Trying to use Hangouts without Gmail is swimming upstream a bit.