I have absolutely no idea what you mean by residents, but since one of the tags you put were "black-city", I'm assuming you mean the people that stand around in Black City that battle you everyday when you talk to them.
The answer, is no, you do not need a Wi-fi connection to connect Black and White games to obtain more "residents". In fact, you can't!
Using the Entralink to go to someone else's game is only doable with a local Wireless connection with two DS's.
What that means is that you will have to be right next to your friend with both DS's on, with the C-Gear on! Your friend must be in any town, and cannot be in any building, with the C-Gear on. You must go to Entralink, and try and pass the world dimension portal bridge thing to the left, or right.
When you are crossed over to your friend's world, touch where White Forest/Black City is on the map below on the touch screen. When you warp there, begin speaking to everyone until you get as many people as you like to your game. Than, you will obtain residents in your Black City! Woohoo!
