Question: where is the best place to advertise my sms chat service? 

Answer: You might check with  Yahoo! Search, I'm not sure but it seems like the most likely place to start as Yahoo! has Small Business sites.  I sort of doubt that a Chat Room would be considered a Samll Business; However, it wouldn't hurt to check, at least it's a place to start.  Good Luck.\nGods blessings to you.
This question from the Yahoo Q&A forum is categorized in the topic: Business & Finance