Grandstream GBX20 Extension ModuleThe GBX20 is an Extension Module that adds functionality, versatility and flexibility to Grandstreams GRP2615 and GRP2624 Carrier Grade IP Phone's and the GXV3350 IP Video Phone. It features a 272x480 LCD display that offers up to 40 contacts per module with support for up to 160 contact s by using 4 modules. The GBX20 supports a wide range of advanced call features including BLF, call park pick up, speed dial, presence, intercom, voice conferencing