Historical clue formulations

• Old telephone service provider, informally — 2018-06-06
• Old phone company nickname — 2014-05-14
• Parent company? — 2014-04-05
• Old phone company nickname — 2010-07-25
• Onetime phone company nickname — 2006-07-10
• With 69-Across, bygone phone message — 2003-08-17
• Parent of Ameritech, Nynex, etc. — 2002-10-17
• Old phone company nickname — 2001-11-19
• Old name for the phone company — 2000-01-31
• Old phone company sobriquet — 1998-06-16
• Onetime phone company sobriquet — 1995-05-30