They had two main branches Nokia Mobiles and Nokia Networks, Nokia Networks eventually joined the networking business from Siemens and thus became Nokia Siemens Networks.

Microsoft did their business with Nokia Mobiles business division, which as we all know they end up acquiring it.

With that money, Nokia bought back the NSN part that belonged to Siemens, replacing Siemens with Solutions on the name.

Many of the people nowadays working for Nokia branded HMD Global phones are actually former Nokia Mobile employees, and the Espoo building is the same I used to visit a couple of times as NSN employee.