Sure. You can get service from a VoIP provider and use it on a single phone without a PBX.
Hi Dicko
Do you have any experience with Kamailio?
I would have to say modestly “yes, a little bit” actually I use a cluster of them as the proxy for dozens of FreePBI, it ain’t easy but is the best open-source sip proxy out there right now, well documented and an active forum.
modestly ???
You even have them clustered, you are an astronaut in my opinion !!
Where did you find the information you needed to get going, and if you have any suggestions I would be very happy to receive any.
Im stepping out on a limp here, but maybe we could figure out some compensation to get us jump started?
We are not ready to pay these guys for 20 hours and still not be sure to get a working product at the end of our 20 hours paid support.
/Kenneth
I also charge by the hour and I am not cheap, so either do your apprenticeship , read the FM and the fora, and save yourself that +$2K, it only takes " not being stupid" and quite a few hours (at least it did for me 
) 
(Stepping out on a limp will always hurt and you will likely be unable to jump very well, see your podiatrist before attempting that ;-))
Hi
What OS should we get to install it on?
Are you running on basic iron or with a hypervisor?
My wife used to be Unix/Linux admin, she might be the resource i need to get things up and running.
I personally use Debian Jessie both for the Cluster and the client machines, if you need a remote , use a NUC or a Raspberry PI (with an external HDD/SDD), depending on your needs.
For the DC’s we use ProxMox 4 over ZFS and glusterfs for HA (seriously, 3 second failover?) ( don’t rely on two nodes. but a third can be a PI, it’s just for quorom) . It takes about an Hour to bring up a new cluster node, about five minutes for a new PBX or Proxy.
We have also sampled VULTR and it reallly makes sense at $5 a month for 20 or so seats and integrates seamlessly.