From Nookipedia, the Animal Crossing wiki
Nookingtons (たぬきちデーパト Tanukichi Depāto?, Tanukichi Department Store) is the largest expansion to Tom Nook's shop. In this expansion a new upper floor appears where furniture, wallpaper, and flooring are sold by Timmy and Tommy, as well as the normal ground floor Tom Nook still runs. In Wild World, it also contains Shampoodle, which provides hairstyle makeovers for players at the cost of 3,000 Bells.
To get Tom Nook to expand his store into Nookington's in Animal Crossing (GCN) and Wild World, the player must spend 240,000 bells and have a friend shop at the store. In City Folk, players do not need a friend to shop at Nookway, and players need to spend only 150,000 bells for Nook to upgrade to Nookington's.
The requirement for a friend to purchase something in a player's Nookway creates problems for those who do not have a real-life friend with a copy of Wild World a second DS with the game, or those who do not have a functional or fast/stable-enough internet connection using the DS's built-in Wi-Fi or a Nintendo Wi-Fi USB Connector (which connects a DS or Wii to the internet through an internet-connected computer), as they will be unable to upgrade their store. There is no other way to upgrade to Nookington's, though one can solve the first problem by exchanging friend codes with another player over the internet – online forums concerning the game will generally feature several people looking to travel and make new friends, with a risk. A second system with a second copy will allow wireless play without the need to connect to the internet. Some Wild World cartridges may also glitch and will upgrade from Nookway to Nookington's whether a visitor shopped at the store or not.
Nintendo has stopped the Nintendo Wi-Fi service, which means that it is no longer possible to upgrade to Nookington's in Wild World using Wi-Fi services, however local wireless still functions, and a friend with a system and game copy allows the upgrade to occur.
In the Wii U Virtual Console version of Wild World, the requirement for a friend to visit was dropped. Otherwise, it would have been impossible to upgrade to Nookington's due to the lack of online functionality.