For regular quality calls (landline quality), it requires 100 Kbps download and upload — with more importance on the upload speed. For HD call quality, it requires 200 Kbps download and upload.
Find you how much bandwidth you have by doing a speed test here: https://www.speedtest.net/
Based on the download and upload speeds, you can divide these by the required bandwidth numbers mentioned above, you will have an idea if your broadband is able to support VoIP calls.
