Aether Systems Inc., a Maryland wireless data company that is selling off its operating units, said yesterday it received a $30 million offer for a division it had already agreed to sell to another buyer for $25 million.

In a securities filing, Aether said it did not pursue the higher offer for several reasons. For now, it said, it would proceed with selling its transportation segment for $25 million to Platinum Equity, a private buyout firm. Aether shareholders are scheduled to vote on that deal Sept. 15.

Aether, of Owings Mills, did not disclose who made the new offer except to say it was from an "investment group." Company executives did not return phone calls seeking comment.

Aether's transportation segment sells services and gear to help customers track fleets of trucks, cars or other assets that are in transit. It is one of three major business lines that Aether has sold or plans to sell as part of the company's strategy of using its balance-sheet assets -- its cash and some tax-related assets -- to buy a large portfolio of mortgage-backed securities.

Aether signed its agreement with Platinum on July 20 and announced the deal the next day. It mailed out proxy materials for shareholders to vote on the deal Aug. 24.

On Aug. 25, the company received the unsolicited offer for $30 million. Aether's board decided that the new offer wasn't enough to make it break its previous agreement. Aether has been trying for more than a year to sell off the transportation division, and the company indicated in its filing that negotiations with the new prospective buyer are uncertain to yield a deal. Also, Aether noted that if it backs out of its deal with Platinum, it has to pay a $1 million penalty to Platinum and reimburse expenses of as much as $250,0000.

Aether went public in 2000 and raised more than $1.5 billion in the stock and debt markets. But its business model to build an integrated group of companies offering wireless data equipment and software has never made money. Last year it began to rethink its strategy, which ultimately led to its decision to sell off its operating divisions and use its leftover cash to invest in a portfolio of securities backed by home mortgages.

Aether also has substantial "net operating loss carryforwards" from the losses it has built up. To the extent it makes money from its new strategy, it can reduce its tax burden by applying those old losses to its new profits. The strategy was largely devised by Friedman, Billings, Ramsey Group Inc., an Arlington investment bank, which will manage Aether's mortgage-backed securities portfolio.

Aether sold its Enterprise Mobility Solutions division to an Annapolis telecommunications company earlier this year for $19 million. Last month, it agreed to sell its government division to another company for $10 million.

Aether's stock rose 2 cents yesterday, closing at $2.95 a share.