[1][2] He was employed (among others) by Nokia Networks and the then Telecom Finland (branded as Tele), as well as Finnet [fi] Oy.
[3] Makkonen played a leading role in creating the mobile communication unit of what is today TeliaSonera.
Subsequently, he worked at the Telecoms and Postal agency (PTL, TeliaSonera) as a systems engineer, developing wireless communications services for the NMT mobile networks (1976–1983).
In 2000, he was briefly the president and board member of the Mobile Internet operator unit of the company, which at that point had been renamed Sonera.
[11] Makkonen was the president and CEO of ICT company Anvia from August 2010 to the spring of 2013 when he left because of serious illness, and later retired.