By integrating your PBX to Green Softech over IP instead of ISDN. Our customizable SIP Trunking service can add VoIP to your existing PBX or minimize your monthly line subscription costs. Most organisations utilise the internet as their primary communications infrastructure, thus it makes sense to use it to carry inter-site voice traffic for free or to replace costly ISDN or PSTN phone lines. Green Softech SIP Trunks are compatible with a wide range of IP phone systems, but we can also SIP-enable your existing PBX without making any hardware change.