Baby Bells See Rivals Taking Fewer Phones  WASHINGTON (Reuters) - Three of the nation's dominant local  telephone companies said on Thursday that they had seen a sharp  drop-off in new residential lines leased to competitors since  AT T Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=T.N target=/stocks/quickinfo/fullquote"&gt;T.N&lt;/A&gt; announced a retreat from residential service  in July due to changing federal rules.