Europe and in fact the world experiences a record wave of telecom merger activity. Mergers are generally expected to create significant value via the realization of synergies – not just in the Network and IT area (remaining the bulk synergy source) but also in Distribution and Marketing, SG&A and – more uncertain – in the revenue area. The challenge for shareholders, lenders and merger / post-merger integration executives is to actually achieve these synergies. This becomes ever more important as synergies tend to justify ever higher proportions of the purchasing price. Our viewpoint provides analysis, lessons-learned, benchmarks, time needed to achieve synergies and hands-on tips derived from a close look at four mobile-mobile mergers in the EU and largely valid for any combination of telecom mergers.