The campaign focuses on AOL's recent price hike, which raised its flat-rate internet access fee by $1.95 (£1.37) to $23.90 (£16.81) in the US.
Microsoft's promotion offers a monthly rate of $21.95 (£15.43), guaranteed until the end of 2002, and three months' free service for customers who switch from AOL before June 30.
In separate news, Microsoft is reported to be in discussions to bundle its Windows Media internet audio and video technology with AOL's internet service.
A deal, if reached, would help Microsoft in its attempt to gain market share from RealNetworks, which is AOL's sole supplier of internet broadcasting technology. The talks are said to still be in the early stages.
www.microsoft.com
www.aol.com
www.msn.com