VOIP gives more flexibility and options to users. UK office landline phone numbers for example can be seen and called by UK clients, while actually working through one’s mobile device. Other advantages include:
Free Inter-Branch or Home to Office Calls.
Massive call savings.
Scalabilty from "2-line Standalone" to "Multiple Line PABX Integrated".
Make any cellphone a free extension of your PABX.
Seamless Integration with Analogue or Digital PABXs.