Yes, it's totally possible.
No, it doesn't require a VPN.
Yes, it's a good idea to have one (although if you're going to want an all-in-one hardware solution you'll need a handset with enough flash memory to contain some open source VPN s/w as well as the SIP stack).
HTH.
Mike.
p.s. - you'd need to look for a broadband connection with decent QoS (and an appropriate router) in order not to sound like Norman Collier.