When Channel 4 moved from Chicago to Milwaukee, Channel 4's former occupant, WBBM-TV Chicago, moved to Channel 2. Channel 2's former occupant, Zenith's experimental "Phonevision" pay-tv service, disappeared.
Simultaneously, Channel 3 moved from Milwaukee to Madison. Channel3's former occupant, WTMJ-TV Milwaukee, moved to Channel 4, resolving co-channel interference with WKZO-TV [now WWMT(TV)], Kalamazoo. WISC-TV lit up on Channel 3, Madison's first television station, and still its only VHF.