Yealink YEA-EXP39 IP Phone Expansion Module
The EXP39 module features a 160×320 graphic LCD and 20 physical keys which feature dual-colour LECs to enhance the ease with which functions are set and used.  A further 20 keys are available via a page switch feature.  In addition the ability to 'daisy chain' up to six modules via RJ11 line cord yields a total capacity of up to 240 programmable keys, each supporting all of the handset's IP/PBX capabilities. These include functions such as SMS, BLF, BLA, paging, speed dialling, intercom and call transfer, park, pick up and return.