The estimates range from 1 to 6 million moving from AT&T to Verizon, although the bulk of sales of a potential Verizon iPhone would still come from current Verizon customers updating their existing phones. The Bloomberg article quotes John Hodulik, an analyst at UBS AG in New York, who comes in "somewhere in the middle" with his projections, saying 2.3 million would switch from AT&T to pick up a Verizon iPhone. Hodulik expects AT&T would sell 8.8 million iPhones in 2011 (down from 15.6 million in 2010) and that Verizon would sell 13.3 million iPhones in 2011. Of those 13.3 million, 10 million would already be Verizon subscribers and the rest would come from other carriers. If indeed Verizon introduces an iPhone later this month, there are still some unknowns that could impact sales. For instance, how much will service plans for a Verizon iPhone cost (typically, Verizon's plans cost more than those of rival carriers) and will the phone offer any new enhancements? Also, despite a lot of AT&T customers being unhappy with the carrier's service, many will be weighing whether to hold out for an improved fifth-generation iPhone that will arrive in June and may support 4G data transmissions. Additionally, AT&T could offer incentives for customers to stick with the company. And finally, perhaps its service will improve as more folks defect to Verizon.