SIP Trunks (or VoIP lines as some people call them) are simply an Internet based telephone line. No longer do you need to install Analogue, ISDN2e or ISDN30e circuits to connect your Office Telephone System to the outside world.
Their are a number of benefits to porting your telephone numbers and lines across to SIP Trunks
Some of those are listed below:
Real time configuration changes
Additional value add services
Lower cost line rental