They're in the process of launching a bring your own phone for Verizon phones. It's not launched yet, but the site will be:
However, they have launched that same service at the sister company, Net10.
Net10 is $5 more a month.
Page Plus does activate iPhone 4s phones - I had a dealer add it for me via eBay. Had it active for half a year without any issues.
Past providers: RingPlus, Page Plus, Virgin, Straight Talk, T-Mobile, Verizon, AT&T.
Past phones: Nokia 820, Motorola Atrix HD, iPhone 4S, HTC One V, iPhone 4, Nokia Lumia 900, Nokia N9, Samsung Focus, Samsung Captivate, Nokia N900, HTC 8525, iPhone 3GS, iPhone, Nokia E61i, Siemens A56...