In 63% of the 50 nations where 4G was available, mobile networks were quicker, said Mr Fogg.
And the gap would only widen once fifth-generation (5G) networks were turned on, because most improvements to wi-fi speeds were set to come from work to upgrade fixed broadband networks, which would take much longer to accomplish.
However, another data speed-measuring company cautioned that it could take a while for the benefits to be shared by all.
“The infrastructure deployed for 5G will likely not extend into remote areas,” Kevin Hasley, head of product at RootMetrics, told the BBC.
“Wi-fi will remain an important tool for the provision of fast internet connections for a segment of the populous.”
Even so, OpenSignal said phone-makers needed to “ensure they do not accidentally push consumers’ smartphones on to a wi-fi network with a worse experience than the mobile network”.
Technology news site The Register said Huawei now made phones that performed tests to find the fastest network.
The report also noted efforts by Samsung to make phones that joined to both wi-fi and mobile networks to send data and boost browsing speeds.
CNN