Right after the new phone is installed, Alice calls Trixie to tell her about it. Immediately after, Ralph comes home and Norton calls from upstairs to congratulate him. But Alice did not give Trixie the phone number, so there was no way Norton could have known it.
The Kramdens' new telephone number is BEnsonhurst 0-7741. But whenever a character says the digit "zero" it is clearly dubbed in and they are actually saying "three".
The phone number of Bensonhurst 0-7741 is clearly dubbed, probably due to the real number being an actual phone number at the time. The dubbing may have been done several years later as Audrey's voice is noticeably more raspy whereas the dubbing by Gleason is more seamless.
There was a second but different dubbing of the phone numbers when Ralph tells Alice he tried calling her at home but it was busy. Both Ralph and Alice say BE 6 7741 originally (Ralph's incorrectly dialed number), this was dubbed to a another 'safe' incorrect number BE 0 7740.
The Kramdens' new telephone number is BEnsonhurst 0-7741, but the "zero" sounds and looks dubbed, as if the characters had originally spoken a different number. (Observation based on the Paramount "Classic 39" DVD set)
The lady tells Alice that the babysitting job is "only three blocks from here" and the address is 383 Himrod St. The Kramden's live on 328 Chauncey St. in Brooklyn and 383 Himrod St. is actually two miles from there.