As a journalist, I frequently view Web demos, using every conceivable technology. GoToMeeting? Check. WebEx? Check. LiveMeeting? Check. Glance? Check.
Wait, you're not familiar with Glance? It's a lightweight, reservation-less system. In my experience, it's the easiest of the bunch to use, and the fastest at initializing a session. It does less than the others, but it seems to do the essentials faster and more easily.
The Glance software offers three options: Start session - show my screen; Start session - view guest's screen; and Join session. The first option allows up to 100 guests to view your screen so that you can demo your software for clients (not to mention press and analysts). The second lets you view and optionally control one guest's screen, which is what you need to do tech support. The third lets you use Glance to join someone else's session as a client instead of using a Web browser; the advantage is that the Glance client is quicker and cleaner than a browser.
What about voice? If it's a one-to-one session, just make a telephone call or run a Skype session in parallel with your Glance session. If it's a broadcast, use the unlimited audioconferencing line supplied as part of your Glance subscription. It isn't toll-free, but the modest cost reflects that.
A Glance 24-hour day pass costs $9.95; a personal subscription costs $49.95 per month, or less if yearly or in quantity; a corporate subscription costs $249 per month for a pool of two concurrent sessions.
I've had good luck with Glance so far for all three functions. I'll consider buying day passes when I need them, once my trial subscription runs out, but obviously if I find myself using more than five days a month, I'll upgrade to a subscription.
Your mileage may vary.