VOIP or properly termed VoIP is almost the antithesis of a traditional POTS or plain old telephone service. The latter uses the usual rollover and hunt group for managing calls and requires that you pay per line. VoIP does not place this restriction on you as you are placing and retrieving calls over the Internet. With VoIP, you pay per seat. While this may seem more expensive, it is like anything else in medicine we all know as risk benefit.
If you have a doctor, receptionist and MA, they will likely all need phone lines unless you are willing to wait for an open line. While you are correct that you can use five phones for example and pay for one line, each person will wait especially if incoming calls are saved in a queue. Your receptionist puts a call on hold which ties up that line and instantly answers the next caller on another line you pay for. So you have to decide how many lines for how many staff. Then there's the DID "direct inward dial" to a phone.
With VoIP, while you pay for each phone or seat, they are logged in separately to your switch and Internet. Any phones and all phones can be used simultaneously. So if you have a phone in your office, you can always dial out. So five phones or seats, it is like having five phone lines. You also have the DID to your phone at all times. Again, you pay per connection, so you could use a phone at home if you wanted and it would appear as though you were at the office. I have a less expensive phone at home and when taking call over the weekend, I turn off a phone at the office via the web portal. I do not need a land line in case my cell does not get a signal. Plus, again, the caller sees your office line. With VoIP while you can put your conversation on hold, you "park" calls for the overall network. You can park multiple calls and not take up a line. There is no line, although there are algorithms or systems so that incoming calls will go to a certain central phone. Other phones can be put into a call group to pick up a call and be changed on the fly. Anyone can then retrieve the call. The flexibility with a good hosted VoIP solution far exceeds the traditional pots rollover scenarios. With a good web Interface, the amount of things you can do are endless.
As with me, it will take a little while to wrap your head around VoIP.
If you do use a hosted VoIP solution where you must purchase phones, etc., hold out for free phones. Also try not to completely disable your current digital phone system until you know the quality is there. You need more bandwidth depending on how many phones and you have to look at having a quality switch that is managed and has QoS. Upload speed is also a factor. When our host company set us up, they came in and spent countless hours making sure every packet made it to the correct destination. When for some reason, Time-Warner (which is blazing fast) was not 100% perfect, they gave us a free SDSL completely dedicated to the VoIP so QoS wasn't an issue. Remember, it is still in its infancy, and there is a lot of competition if you go with a hosted solution. So, act interested, then hold out, then start to purchase, then ask for free phones (some range up to $500 -- especially Cisco phones). The application on our receptionist's desktop is very cool. Calls come in, you see the name and number via CallerID. You can park them with your mouse, drag and drop to another phone, etc.
