I have a trademark on "Messenger Plus!" which means that I can legally challenge anyone using this name, even without the exclamation point. For the record, eFax is
trying to register this name and they won't succeed (they gave me some troubles two years ago and I'm not about to forget about it
).
As far as I'm concerned, I don't care about othercompanies using "Messenger Plus" as long as it does not conflict woth my own software. Nobody has anything to earn in that kind of legal issue so I prefer to keep it simple. The only reason why I actually registered a trademark is to defend myself against comapnies like eFax that want to profit from the success of others.