The rivalry between Apple and Google has intensified with Apple buying the mobile advertising business, Quattro Wireless.
The purchase puts it in Google's own business arena of advertising - on the very day that Google squared up to Apple on its own home turf.
Google on Tuesday launched its smartphone, Nexus One, which is designed to challenge the iPhone.
Apple would not say how much the Quattro deal was worth.
Reports suggest it could be around $275m (£170m).
Apple's spokesman, Steve Dowling, said: "We look forward to developing exciting new opportunities that will benefit Quattro Wireless customers in the future."
Head to head
Quattro's advertising network spans mobile Web sites and applications. The company is a competitor to AdMob, which Google agreed to buy in November for $750m.
The release of the Nexus One is seen as a move to ensure Google remains relevant as people search the web using mobile phones rather than typing queries into a PC.
Google makes the lion's share of its revenue by selling adverts linked to those queries.