Corrected entry: The story goes back 16 years. Walt and Skyler are visiting the house they would later buy and the realtor decides to leave them to go to the car and "make some phone calls." But there would be no cellphones back then.
Correction: Breaking Bad takes place between 2008 and 2010, so if we go back 16 years, that would place the flashback around 1992. Aside from the other correction mentioning car phones, cell phones did indeed exist in 1992.
Corrected entry: The silver car that Mike drives shows a New Mexico license plate to the rear, but Texas inspection and registration stickers on the windshield.
Correction: A lot of cars in New Mexico are inspected in Texas before being imported there.
Corrected entry: During the scene in which Gus is talking on the phone with a "colleague" of his, the boss of the two assassins who shot Hank, it is night time and the surroundings outside of Los Pollos are dark. However, when gunshots are being heard in the background and Gus snaps his cell phone in half it is daytime. The sky is blue behind him and the sun is shining off of his head. (00:43:10 - 00:45:00)
Correction: The "sky" in the background of Fring's head is the lights of the restaurant. The "sun" which is shining off his head is the light post under which he is standing. The scene is and remains completely in the night.
Correction: Carphones have existed for many years, certainly around the time period referenced here. They were prevalent by the 80s. https://en.wikipedia.org/wiki/Car_phone.