AT&T (T) - Get Report was down 3.3% in midmorning trading after saying it will delay an offer to exchange its own shares for shares of AT&T Wireless (AWE) , citing a paperwork error.

The telecommunications giant also said it will retain up to $3 billion of the wireless unit's stock. The exchange, which was to begin next month, is now expected to start in early April. AT&T blamed the delay on the inadvertent omission of some financial data from an electronic file transfer to the

Securities and Exchange Commission

. AT&T Wireless was down 6.1%.