No you don’t have to change your number.
Customers that call your existing line can still reach you. You have spent a lot of time and money advertising that phone number to customers and Access Point understand it is not easy to change that number. Additionally, keeping your existing PSTN number will mean that if your VoIP provider ever goes down you will still be able to make and receive calls over that line.

VoIPShop.com.au recommend most businesses keep at least one of their existing PSTN lines (commonly the advertised number customers use). This will allow customers to call in on the known number. VoiPShop.com.au also recommend signing up with a VoIP provider, this will allow you to start saving money on outgoing calls. There are several options to incorporate VoIP telephony into your business, and most of these options do not require you to have your business solely run on VoIP. However, many businesses are successfully running their phone system, fax and EFTPOS solely over VoIP. VoIPShop.com.au can help to design your networking solution to cover your personal requirements.