In the UK, 8% of ad impressions in November were on WiFi networks, according to mobile advertising network AdMob, up from 4% in August.
More than half (56%) of these came from the iPhone, which is higher than most mobile handsets, which usually drive 10-20% of requests.
Similar growth was recorded in the US, with 8% of total requests on Wifi networks, compared to 3% three months ago. As many as 42% of impressions are coming from US iPhone users.
Worldwide, iPhone impressions grew 52% month over month, to 359m in November, giving the iPhone 6.3% of total requests.
In its monthly mobile metrics survey, Admob revealed the inclusion of WiFi on popular new smartphones such at the G1 and BlackBerry Bold will only push WiFi growth further.
After the iPhone and iPod Touch, the Nokia N95 and other N series phones are the leading WiFi devices in the UK.
Mobile devices that aren't phones, such as the Playstation's PSP, are also generating notable WiFi traffic.