Agere to Cut Another 500 Jobs  CHICAGO (Reuters) - Communications chipmaker Agere Systems  Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AGRa.N target=/stocks/quickinfo/fullquote"&gt;AGRa.N&lt;/A&gt; on Wednesday said it will close a Florida plant  that employs 600 people if it cannot find a buyer by December  2005 and cut an additional 500 jobs amid slowing sales.