I use SIP phones in our own office and they are great! SIP phones are simply telephones which plug into the Internet instead of your phone line; they allow you to receive phone calls from the normal phone network just like a normal phone and you can dial out to the real world too, normally on really cheap dialing tarrifs. The best bit is... inter-SIP calls (Calls to another SIP user) are totally free so we could install SIP phones in your two Branch Offices and Head Office and wave goodbye to your internal phone bills! And if that's not enough, you can unplug the phone and plug it in at home and take the number with you so moving offices is no-longer a royal pain in the backside with calls diverting all over the place!
You can make savings too with a SIP phone, even if you've got just one phone, but the savings will really start making sense with two or more users. You can make use of call-centre type features at a fraction of the cost, such as call-queuing, multi-ringing, timed diverts, voicemail to email, remote calling, etc.
SIP phones generally work by connecting across your Internet link to a hosted SIP exchange (probably somewhere on the Isle of Dogs ) normally for free with your dialplan. But if you've got over 10 users or already have a PABX exchange then it makes sense to implement a Local VoIP Server in your organisation. This gives you full control over the exchange features and allows you to integrate existing land-line telephone numbers.
For more information or a quote for new SIP hardware or installation then please contact me.