It depends on which type of headset you will be using.
The Plantronics Spare part called an Adapter, Plug Amp, Spare #18709-01. allows you to use modular headsets (and wireless systems) with a plug prong phone.
The P10/2250 (formerly SHS1761-12) amplifier is a modified version of the P10 amplifier that is used only on the Meridian 2250 console. H-series headsets are the only headsets compatible with the P10/2250.
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Always check the compatibility guide first to see which item your telephone requires.