In April 2005, we purchase a domain name with three extensions. The domain name (without the extensions) was to be used as the tag line for our educational services business and for our book series. We plan on starting our business in a month. Today we discovered that this tag line is also being used as a tag line for an educational services conference and that it was registered as a U.S. trademark by them earlier this year n California. In our Google search, several people use this phrase and it is also the name of a company in California. Can we legally still use our domain name (without the extensions) as our company's tag line and as the title of our book series?