AT T, Vonage Cut Prices on Internet Calling  WASHINGTON (Reuters) - AT T Corp. &lt;A HREF="http://www.reuters.co.uk/financeQuoteLookup.jhtml?ticker=T.N qtype=sym infotype=info qcat=news"&gt;T.N&lt;/A&gt;  and Internet  telephone provider Vonage on Thursday said they were cutting  prices for their residential Internet calling services by \$5  per month, the strongest signs yet of a price war in the  nascent market.