Hailed as offering speeds many times faster than 4G – downloading an HD film in seconds – the technology also comes with significant costs.
Energy use is three times higher and, with a shorter range, it needs a near tripling of masts, although masts will be smaller.
SFR has already started testing a new 5G network in Nantes and Toulouse, and has suitable phones from Samsung, Huawei and Xiaomi.
Operators say 5G will have almost endless uses in connected devices, tele-medicine, self-driving cars, education and farming, but some experts warn that costs are being ignored in the rush.
Hugues Ferreboeuf, of digital thinktank The Shift Project, says that with calls to cut carbon footprint, the need for a complete rebuild of the network, with higher energy usage and expense, plus increasing cyber-security risks, is unwise.
The possible impact of 5G on certain health conditions has also been acknowledged by medical authorities.