Nokia climbed up the value chain in their vertical. From telephone cable into PCM line concentrators. From those into small exchanges. Then to the DX-200 digital telephone exchange. They merged/bought Televa (small exchanges and Gen0 Cellphones) and bought out Salora from Mobira (Gen0 cellphones and commercial radios). When Gen1 NMT became a thing they started making phones for it and later basestations. With GSM (Gen2) they ware making basestations and handsets from day one.

And they still make basestations and exchanges to this day. So they kainda are at their roots.