Thursday is Verizon iPhone day, and AT&T is celebrating with a tempting offer that may keep many of their iPhone customers out of Big Red’s clutches -- a new, free calling feature called AT&T Messaging Unlimited with Mobile to Any Mobile Calling. The only catch? You need to have (or add) unlimited text messaging.

ars Technica is reporting that AT&T has launched a new calling feature, ironically timed on Thursday, February 10 -- otherwise known as “VI Day,” the day when the general public can finally get their hands on an iPhone from Verizon Wireless.

AT&T Messaging Unlimited with Mobile to Any Mobile Calling is the jilted carrier’s latest attempt to hang onto their iPhone customers, and it’s actually a great deal if you’re one of those people whose friends refer to them as “Chatty Cathy.”

If you already have unlimited text messaging and a qualifying voice plan (more on that in a moment), all you have to do is visit AT&T’s website and add the Mobile to Any Mobile Calling feature -- now you’ll get unlimited calling to any other U.S. mobile number, regardless of which carrier it’s on.

If you don’t currently have unlimited text messaging, you can add it and still qualify -- AT&T charges $20 per month for individual plans or $30 per month for FamilyTalk plans. You’ll also need a qualifying voice plan, which includes Nation 450 and 900 as well as FamilyTalk 700 or higher.

Other than that, the new feature works exactly as advertised. After adding the feature, calls to landlines will be the only time you’ll consume your monthly (or rollover) minutes -- and let’s face it, these days most everyone has a mobile phone, so this is a pretty great way to talk more without spending more.

New and existing customers can sign up for Messaging Unlimited with Mobile to Any Mobile Calling by hitting AT&T’s website starting today.

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