Good bandwidth makes the difference between VoIP that sounds terrible and jerky (and is not worth it) and VoIP that sounds every bit as good as your regular telephone.
When you are looking at bandwidth for VoIP on your mobile computer, you need to think about two network segments (see Part IV, "Your Own Wireless Network," for more information about how these different parts of the network interoperate):
There's not a whole lot you can do about the first of these, the Internet connection, other than try it and see. But as a ballpark, any decent broadband Internet connection should do.
The connection between your mobile computer and the gateway to the Internet (the access point or router) is a closer thing. Probably, 802.11b Wi-Fi is not good enoughbut 802.11g is. In the wired world, 100BASE-T Ethernet will almost certainly do. (But 10BASE-T Ethernet is too slow.)
A useful way to test your connections for their capability of handling VoIP is the site provided by Brix Networks, TestYourVoIP, http://www.testyourvoip.com, shown in Figure 6.4.
Figure 6.4. You can test your connection to the Internet for VoIP readiness using TestYourVoIP.com.
TestYourVoIP allows you to run tests of connectivity speed for VoIP to a variety of locations. For example, as you can see in Figure 6.5, my VoIP connectivity from Berkeley, California to Helsinki, Finland is "better than a decent phone call," but not quite "as good as calling next door." In other words, it will probably do.
Figure 6.5. My VoIP connectivity between California and Finland will probably do for all but the most picky.