Grandstream GXP2200EXT Extension Module

Quick overview from the supplier:

Grandstream GXP2200EXT Extension Module, 20 Buttons, 40 Contacts, Black // Supported by the GXP2140, GXP2170 and GXV3240 128x384 backlit LCD display 20 programmable dual-color buttons per module, 2 pages per module (40 contacts total) BLF/speed dial Daisy-chain up to 4 modules for up to 160 contacts/extensions BLA (bridged line appearance)/SCA (shared call appearance), BLF (busy lamp field, standard or eventlist), Call Park/Pick-up, Speed Dial, Presence, Intercom, and conference/ transfer/forward and more