The two companies will form a 50-50 joint venture called Nokia Siemens Networks, with predicted sales of E16bn and cost savings of €1.5bn (£1.03bn) a year by 2010.
The new company will employ 60,000 people and is expected to be up and running by January next year.
Simon Beresford-Wylie, executive vice-president and general manager of networks at Nokia, will be chief executive officer of the new company.
London M&A partner Jonathan Coppin is leading the Shearman team advising Nokia, which includes partners Iain Scoon and Ian Nisse in London and partners Georg Jaeger and Heino Rück in Mannheim.
Clifford Chance partners Peter Charlton and Joel Ziff are advising the Siemens in-house legal team.
Dr Lutz Englisch, head of the M&A transaction group at Siemens, and Nokia general counsel Carl Belding, along with M&A director Susanne Mattsson, are the key in-house lawyers on the transaction.
Faith Dickson of Sackers is providing pensions advice. No lawyer could be contacted before going to press.