I would recommend for a VOIP client something called imVOX. It's a powerful, compact, Amazon AWS cloud-server-based VOIP client that, based on my own experience as well as those of my friends, works like it claims. How do I know? Both my friends effectively have dial-up connections, yet their voice quality is just as good, if not better than Skype! Not only that, they remain connected until they decide to leave the voice server or their computers crash, even during long, 1-2 hour sessions! Here's just some of its features:
-Only uses 1-8kb/s for professional-quality voice (I can confirm via the Windows 7 Resource Manager that it only uses 5kb/s on my end).
-Outrageous connection stability.
-Servers and client are extremely reliable - your computer is more likely to crash than your imVOX voice server or client.
-Has a free account that doesn't compromise on voice quality.
-Any account can host a 30-person voice server.
-Eventual addition of software-based voice modulation - no fancy sound card required!
-Minimum requirements: Pentium III 850MHz, 512MB RAM, Windows XP SP3
For more features, check this out. For an FAQ, check this out, too. Should you want to contact them, including for technical support, go here.