The project aims to reach 1 million households within five years, it said.
T-Mobile competes against KPN and VodafoneZiggo in the Netherlands.
In March, KPN announced a 440 million euro partnership with pension fund giant ABP to speed up its fibre optic rollout, targeting customers in under-served areas.
KPN, which says it already reaches one third of the Netherlands' 8 million households, plans to reach another 2.5 million by 2026.
($1 = 0.8417 euros)
(Reporting by Toby Sterling; editing by Jason Neely)