Sprint Up, Nextel Down on Merger Talks  PHILADELPHIA (Reuters) - Shares of Sprint Corp.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=FON.N target=/stocks/quickinfo/fullquote"&gt;FON.N&lt;/A&gt;  jumped on Friday as the telephone company continued merger  negotiations with Nextel Communications Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=NXTL.O target=/stocks/quickinfo/fullquote"&gt;NXTL.O&lt;/A&gt; for a  deal that would combine the No. 3 and No. 5 U.S. wireless  service carriers.