There are many ways to use VOIP, some leveraging Google's pre-beta GrandCentral service. It's taken about 14 years longer than expected, but we're finally moving to non-metered worldwide voice communication.
I've been using Google's GrandCentral with my iPhone's GrandDialer to phone my parents in Montreal. The call quality has improved dramatically in the past months, and the (still) free services is paying for my data plan.
The recent call quality improvements in GrandCentral suggest Google is going to stop using GrandCentral to cow the phone companies, and actually bring it to market. That won't help AT&T's numbers, and it might be the death blow for Sprint.