Can 2 people use the same wi-fi system and use the radio to talk to each other?
More detail/explanation of yuor situation will yield a better and precise answer.
If you're on a LAN via hard cable or WiFi and playing on a private arena or in the MAs with another player, yes, after properly setting it up and understanding implemented restrictions (IE: range only broadcasts to friendlies within a certain distance/range of you while you're in flight. Tuneable vox only works if you and the other player(s) are tuned in on the same vox frequency/channel - this can be done a number of ways such as directly with another player (type in their name/handle into the field) or a numbered channel between 100 and 299 (NOTE: 100-199 is friendly/same-country only, 201-299 is "all". IE if you and the other player are on opposing countries, select a channel in the 2__ range, otherwise they are intentionally "protected"). Also, be sure to tune to yourself first (type in your own name/handle in the vox channel field) and make sure your settings are right and you can comfortably hear yourself.