The trademark wasn't filled until February 2010. http://tess2.uspto.gov/bin/showfield?f=doc&state=4003:5a...
The trademark is for the concatenation 'whoshere'. Given that both are common words obvious to the topic I would have thought the interpretation would be very narrow and 'who's near me' is suitably different. I certainly don't think you should give in to their somewhat extortionate demands.
"Red" and "Hat" are common words too, but you'd never get away with trying to sell a linux distro named "Red Cap".