yes you can do this. A VPN would definitely work for you.
Though you may run into quality issues. Unless you have some type of Quality of Service ALL THE WAY between sites and all networks in between you cannot guarantee call quality ever… end of story.
I personally use 501s/601s for my personal use at home VPNed to my main site, but I only use that for personal use. “Business sites” are interconnected via private MPLS based networks from a single provider with strict priority queing for VoIP traffic. some may say it’s overkill… but if you don’t do it that way… wait till people start smacking the network or your internet providers network gets hammered… and then people start losing quality or dropping calls… it’s not a pretty situation especially if you have to support it… for some reason people expect voice traffic to be 100%
still going over arbitrary internet lines is generally fine for personal use, or even small scale business use… as long as the people “buying into” the service understand the limitations and possible quality issues upfront, and it doesn’t come as a surprise to them later when they get stuttering on calls or even dropped calls.