I have confirmed hearing a Taxi Company serving the Essex county area on 157.630 MHz. Perhaps that's them! Let me know if it is. A good idea is to just drive near the company's headquarters, park your car nearby, and see if you can pick them up using the close-call option on your scanner. That's how I got several of my frequencies in the past. I've found that many taxi companies do not license themselves with the FCC and/or they buy radios from radio rental companies. For example, Linden Yellow Cab isn't listed in the FCC database, however they do use frequencies in the 504 - 505 MHz range from a recent close-call I captured on my scanner.