Google’s Android mobile operating system won its most significant endorsement to date as Verizon Wireless agreed Tuesday to launch a series of wireless phones, netbooks and PDAs that are based on the open source platform. The announcement by Verizon, the nation’s largest wireless carrier with 87 million customers, leaves AT&T as the only major U.S. mobile phone company that has not publicly stated its intention to offer an Android device. (However, sources close to Dell, Inc. said unofficially on Wednesday that the computer maker is preparing to enter the U.S. cell phone market next year with an Android handset that would operate on the AT&T network.) Now offered by 32 carriers in 26 countries, Android wireless devices entered the U.S. through an agreement signed one year ago between Google and T-Mobile USA, which currently markets two Android models produced by HTC of Taiwan. Sprint Nextel, which adopted the system earlier this year, is expected to roll out its first Android handset next week. Although Verizon has not identified the manufacturers of its Android handsets, Verizon Wireless CEO Lowell McAdam said his company intends to launch two Android phones by the end of this year that would constitute the first in “a family of devices.” In contrast with Apple, Inc. and AT&T (which, reportedly, are still studying the suitability of Google Voice for the iPhone), McAdam also confirmed that Verizon’s Android handsets will support the Google Voice application. Describing Google’s partnership with Verizon as “a major milestone in the development of Android,” Google CEO Eric Schmidt called the agreement “a very big deal for us.”