Go to the safe house that Roman gives you (or Playboy X's mansion after killing him for Dwayne).
Enter the safehouse and enter 267-555-0150 into your cellphone 6 times to get a six star wanted level and wait for 5 minutes (away from the window in the safehouse due to helicopters shooting you if you get seen by them.
After you have the achievement go to your bed and sleep (save game) and your wanted level will disappear.