I have a hobby for collecting old phones. Recently, I have acquired both an iPhone 4 and iPhone 4s that work perfectly. A buddy of mine said if I unlock the phone, there are ways of using it on my current call and text plan (AT&T US) that I have a flip phone on by simply unlocking it and switching the sim card. That way I could have internet where there's Wi-Fi, and calling and texting everywhere on the same device without paying data charges. Is he right? If not, is there any other way of getting that result such as using a pay as you go plan? How hard is it to unlock an iPhone 4 or 4s? My cousin did it to his so he could teach me right?