I wouldn't say ONLY because if there *is* another pc-guy out there by the time the phonebook comes out, you could be in trouble.
I'd use something that implys it. Something like "Native Phillidelphian" or "Born and Bred Right Here in Philly!" Or, as long as you don't speak any second languages, go the other route and say "Service available in english-only, sorry." Make it sound like you're apologizing for not speaking Farsi or Mandarin, when in fact it also states that you ONLY SPEAK ENGLISH.
Sounds like my last search for a doctor... I have to go to a specialist, and most of them around here are Arabic. Now, I have no problem with an Arabic doctor, except the one I'd tried to go to had a language/culture barrier. She knew my words, but she couldn't understand my situation (working 12 hour shifts at night, staying up all day to take care of my ill mother, only sleeping every third day, at night). So I looked up a list of all the endocronologists within 20 miles of my zipcode, and two euro-american-sounding names came up. One was the first doctor I used to go to that if I ever see again I'm likely to inflict physical harm upon, so skip him. The other was the one I called and have been happy with ever since.