Virgin Making Mark Among Mobile Services  NEW YORK (Reuters) - When Virgin Group &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=VA.UL target=/stocks/quickinfo/fullquote"&gt;VA.UL&lt;/A&gt; Chairman  Richard Branson put his brand on a U.S. mobile telephone  service two years ago, there appeared to be scant space for  newcomers to the crowded market.