Although taxis roam the city quite frequently, it's far easier—and certainly safer—to order a cab through your hotel (if you call on your own, keep in mind that getting an English-speaking operator is hit or miss). Most taxi companies will give you a price in advance. There's sometimes a delay, but usually the cab arrives within 15 to 20 minutes unless it's late at night or rush hour; the company will phone you back when the driver is nearby. If you order a cab this way, you pay the official state fare, which is quite reasonable by U.S. standards. No tip is expected beyond rounding up the amount on the meter.
If you flag down a taxi in the street, fares vary according to the driver's whim; you're expected to negotiate. Foreigners can often be charged much more than Russians, and oblivious tourists tend to be gouged. Make sure that you agree on a price before getting into the car, and try to have the correct money handy.
Petersburg Taxi (068.)
Taxi Million (812/700–0000.)
St. Petersburg is a large city of 5 million inhabitants, and petty crime is a problem. As a foreigner, you're an even more likely target for pickpockets, especially in the metro and in and around Nevsky prospekt. Watch belongings carefully in such areas, and be careful when using your phone. Thieves have been known to grab mobiles and similar devices while their owners are distracted. Be attentive, leave valuables in the hotel safe if you can, and carry those you need to take with you in a money belt or at least in a front pocket, preferably zippered.