My office has just had fibre installed in our street (in Auckland) and I'm looking at upgrading our ancient telephone system to a voip system (and hopefully save some money).

We currently have three copper phone lines into the office, and two phone numbers (phone and fax). If one line is used then the system switches to the next available line. We rarely have more than three calls at once in the office so that suits our current needs.

We currently still receive orders via fax so can't do without it yet. We've been told by Vodafone that we will need to keep the copper fax line as other options including fax to email are unreliable.

Our alarm system (probably 10 years old) still dials the monitoring company using the fax line.

If we upgrade, do we need to have the equivalent number of VoIP ‘lines’ into the office? We would still want to advertise our primary phone number as the only number, but be able to take more than one call to that number at any one time.   

Essentially we would still like to have a single phone number but be able to answer it from any of the 5 extensions in the office, then transfer the call to any other extension (we don’t have a receptionist so everyone needs this ability). At the same time we need to be able to take second and third calls into the office on the same number.   

Thankfully our office is cat5 cabled.

I see similar questions have been asked before but none too recently. From my initial reading it appears that a cloud based service such as 2talk would probably do the job but any recommendations would be most welcome. I'd also welcome recommendations of Auckland comms companies who would be capable/interested in helping us.