Twitter is launching an adverts service according to a posting on the All Things Digital Blog http://mediamemo.allthingsd.com/20100226/twitters-ad-plan-copy-google/

The adverts services will launch in the second half of 2010. The ads will be 140 characters or less, the same maximum length of a tweet and will appear when users search for keywords eg iPhone.

Still lots of details have not been disclosed but we will keep you posted.