Quick overview from the supplier:
Grandstream GXP2200EXT Extension Module, 20 Buttons, 40 Contacts, Black
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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
https://www.grandstream.com/products/ip-voice-telephony/extension-modules/product/gxp2200ext-expansion-module
