Grandstream GRP26XX Carrier-Grade IP phones support the VPK (“Virtual Multi-Purpose Keys”) feature to add more flexibility and provide better user...

Busy Lamp Field (BLF) feature allows an end user, such as attendant, to monitor the hook status of a list...

Although SIP protocol (RFC3261) was not providing the semantics to support the Busy Lamp Field (BLF) but there’s a way...