Phosphonate‐substituted iminium salt 2 was used in Mannich reactions with various nucleophiles to obtain novel α‐aminophosphonates. This straightforward and efficient methodology has a broad scope and provides highly functionalized Mannich bases (4 and 8). Furthermore, vinylic, aromatic and homoallylic α‐aminophosphonates (5, 10 and 12) were synthesized in good yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)