In order to call a taxi, position Niko near traffic, preferably somewhere on the sidewalk. Spot a cab and press the LB Xbox 360 or L1 PlayStation3 . Niko will automatically call out for a taxi. It is also possible to order a taxi with the cell phone if you have problems spotting one. Additionally, Niko can eventually earn the ability to call a limo as you progress in the game.

Don't Pay Toll
If you approach a toll booth with an emergency vehicle (sirens on), the gate will open and you'll avoid paying $5.

Call the Police!
If you press LB while in a police car (stopped), you can call for backup. Officers will come to help you (though they'll turn on you when they realize you're not a cop!).