T&T won't let you get an iPhone data plan without voice minutes, so at the very least, you've got to pay $40 per month for 450 minutes. If you're not routinely talking for longer than that, Skype probably won't help you. Still, consider having long phone conversations over Skype just to reduce the chances of going over 450 minutes. This will help you collect rollover minutes as well.

Things get interesting when you regularly exceed 450 minutes per month. To truly replace your expensive voice plan, you'll need both a Skype subscription and an online number (formerly SkypeIn), which any phone can call.

Long story short, you can pay $60.48 per year, or roughly $5 per month, for unlimited calls to and from your Skype number. So instead of paying $60 for 900 AT&T minutes or $70 for unlimited minutes, you'll pay $45 for a basic 450-minute plan and Skype.

More: More: http://pcworld.com/article/201659/