Right now today no you do not need VoIP but very shortly the networks are going to change and you calls will all be VoIP anyway, as this change happens it will become very quickly apparent that it would make sense to not be connecting via old methods but instead to directly connect and talk the same language which will be IP and a protocol called SIP.
Don't take our word for it find out for yourself when your existing phone lines, ISDN and Broadband services are due to migrate to the new network (21CN) by clicking here and finding out when you are being "Switched on".
VoIP is low quality cheap calls Right?...
WRONG! In the early days people had small connections to the Internet and so they found ways to compress your voice down and get up to 8 times the calls across the same lines to cut costs, the result was very bad call quality with a constant hiss in the background. The networks were also not ready for VoIP and you got 'jitter' that's wh-n y-u st-rt l--sing sp--ech (when you start loosing speech). This to most was what they expected from VoIP an inferior quality but cheaper.
Welcome to Enhanced Voice and High Definition Sound, now we can do something unheard of and actually increase the quality of calls as the limiting factor has always been the legacy PSTN network but remove this and send a call end to end in VoIP and you can actually select the calls to be in a higher quality (you can control it) and hear things like bass for a more natural sound.
And with the costs of high capacity connections constantly falling then yes you can still save money but this time improve quality in the process.