Installing a traditional phone system in your business requires investing in expensive equipment to facilitate communication. This, along with previously mentioned maintenance costs, can be expensive. Fortunately, VoIP solutions do not require any of these.
You can use just about any hardware you currently have to start using it. The only time you will invest in any expensive equipment is to upgrade your speakers, microphones, and the like to enhance your VoIP system. It is up to you whether you want to opt for these upgrades, so you can delay them until you are financially able to afford them.