The GBX20 is a backlit LCD extension module supported by the GRP2615, GRP2624, GRP2650, GRP2670 carrier-grade IP phones as well as and GXV3350 and GXV3450 IP video phones. The module includes 20 dual-colored extension keys and 2 arrow keys for page switching (allowing each GBX20 to support up to 40 contacts/extensions.). Connect up to 4 GBX20 modules to compatible Grandstream phones for a total of 160 contacts/extensions.