In short, and what Phillip has told a thousand people previously, if you regged the name with prior knowledge of the .com or if you attempted to sell your domain to the owner of someone who has built some kind of intellectual property on the name (including the .com in this instance) then it's irrelevant that he has no filed TM, you are a cybersquatter and yes, he can sue you for infringement.
Dont worry, it's a mistake thats been made a zillion times before you. Your best best bet (unless this domain which youve registered is Uber generic) would be to say "hey ive had second thoughts, sorry for your trouble, here's the domain for free"..
My suggestion is to cancel the domain, if it's less than 5 days old - you will need to work fast - contact the registrar to request them to cancel it because you made a mistake registering a TM domain - they may even refund you your registration fee.
If the domain is older than 5 days, then you have some options - if it was me, I'd simply remove all my contact info and then delete it. Alternatively, you could give it to the company - many people advocate that option, but I don't ... less interaction, the better.
You don't have to have a "", Registered Trademark to have a legal trademark. All you have to do is use the term with "TM" after it to claim an unregistered TM or SM for a Service Mark which is for non-tangible goods and services.
Read here: http://www.uspto.gov/web/offices/tac...c/register.htm.
Also, just because you can't find a U.S. Registered TM, doesn't mean they don't have a registration from one of many countries that are honored by treaty...
Not to sound too mean here, but that answer is everywhere around here. Trust me, if you do what I aks (yes, you have to put the time into it to learn and understand.). Just about everything has been covered...
I feel sorry for you. Better luck next time...