Pardon my ignorance but......my son lost his iPhone 6 & is currently without a phone. He is away so, that is problematic. I have an old iPhone 4 that I want to give him. I have & the 4 was purchased when I had AT&T. My son is on wife's Verizon plan. I know newer iPhones can be activated using the provider of one's choice but, is that true of an older phone like the 4? Can this phone that was previously active on AT&T now be activated on Verizon? Thank you