Using the iPhone for Magic Jack and saving money?

I have an iPhone 4S. I have been an iPhone enthusiast from the very beginning. I'm not sure I will ever use a different phone.

I also have a Magic Jack account, that I have been using for years for my business. At $20 a year, it is by far the most economical way to make phone VOIP calls. It's brilliant and I enjoy the freedom and security I get from having an extra phone line while keeping my private (iPhone) line private.

But prices for iPhone plans are prodigious, ridiculous, and with the economy being the way it is, I'm having an awfully difficult time keeping up with my AT&T cell phone bill every month. I have two iPhones on my plan, and because I can't get Internet in the area where I live, I'm also forced to have a Mobile Share Plan. My bill every month is about $250, give or take. That's a lot of money to pay for two cell phones.

There's a Magic Jack iPhone app. It uses your data plan to make phone calls, and it doesn't require a cell phone service at all. Once the app is on your phone, you could remove the SIM card from your iPhone and never need a wireless carrier again, as long as you have Wi-Fi. As I've already mentioned, I don't have Wi-Fi, so I must have cell phone service.

So my thoughts are trying to marry my iPhone data plan with the Magic Jack. Since by necessity I have a mobile share plan, why couldn't I simply lower my minutes on my iPhone talk time to the lowest possible and simply use Magic Jack for my calls? I would not be using my AT&T minutes when making or receiving calls through the Magic Jack app, which makes use of the AT&T data plan, not the cell phone plan.

Minute for minute, using the Magic Jack app to make calls over the Internet would be cheaper than the same number of minutes you'd use in regular cell phone service, right?

If this is true, what is the absolute LOWEST number of minutes I can opt for my iPhone? I have unlimited texting and 15 GB of a mobile share plan, which the Magic Jack app will make use of.

Added (1). I'm specifically referring to the iPhone app for magic jack. Could I conceivably get the absolute lowest rate possible for talk time from my AT&T carrier, using magic jack instead, and save money making calls using my 4G data plan? If it is cheaper to use my data plan for my calls (magic jack uses Wi-Fi or your 4G network to make calls), I would lower my talk time plan with AT&T and simply use the magic jack app to make my calls.

And does anyone know what the lowest AT&T talk time plan there's? AT&T's website is undergoing maintanence.

I'm guessing you must use alot of day minutes, as I haven't had a landline in years and use the iphone for everything (for me its actually cheaper since I dropped the landline completely). There are some better calling plans so you may want to look around at that also as long as they have service in your area and the areas you travel most, etc.

This is a really good deal for example:
Starting on January 11, 2013 in more than 2, 000 Walmart stores and online at Walmart.com, customers now have access to the iPhone 5 and iPhone 4 on Straight Talk's $45 no contract unlimited talk, text and data plan. To make this offer even more affordable, Walmart will be offering customers who purchase the phone in the store, a no interest fixed-monthly payments special financing offer for only $25 a month with a Walmart Credit Card.

Umm, is this a question or an advertisment?