For only 2-incoming lines, I use a Linksys SPA2102-NA VoIP ATA phone adapter with my BYOD (bring your own device) VoIP services.
If you require 20 outgoing lines, you may consider an IP-PBX system from 3CX Corp. They provide a free version for small installation testing.
For do-it-yourselfers, VoIP can be a bit complex when first getting started.
I have a website that is a good resource for the layman just getting started using VoIP.CQVoIPhttp://www.cqvoip.net