Sprint, Nextel to Build on Wireless Strength Proposed merger would create the country's third-largest wireless unit, and the new company could be a very formidable competitor given Nextel's prized customer base. &lt;FONT face="verdana,MS Sans Serif,arial,helvetica" size="-2" color="#666666"&gt;&lt;B&gt;-The Washington Post&lt;/b&gt;&lt;/font&gt;