The Verizon iPhone 4 officially went on sale this morning at Apple, Verizon Wireless, Best Buy, and select Walmart retail stores across the U.S. Based on early reports, it seems that Apple’s and Verizon’s strategy of tiered pre-orders—existing customers on February 3, all others on February 9—seems to have kept launch day lines at retail outlets manageable. The International Business Times reports that only eight people were…