That's pretty clever, and appears to be already in use even for 4G.
"Swisscom and Ericsson have proved that city manholes can be used worldwide to improve capacity with small cells – even below street level – using the Ericsson Vault Remote Radio Unit and Kathrein’s Street Connect, an in-ground microcell antenna system. The use of existing street manholes where fiber and power already exists lowers total cost of ownership by 50 percent.
This, the world’s first vault site for LTE and small cells has been approved by the Swiss authorities, and 250 new rollouts are due during 2016 in the country’s cities. The solution effectively addresses cities’ needs by enabling the reuse of existing assets and underground space."
Really since 2016. Good framing by Voda to present this as "Building on its heritage of innovation".
[0] https://www.ericsson.com/en/news/2016/3/swisscom-and-ericsso...