Hello! Can you tell me if this works with VOIP phone systems? Do your desk phones need to have a Page button?

This version works with a VoIP or a digital system. You can simply program an extension to it. You'll also need and ATA adapter. This will convert the SIP signaling to Analog. Contact us directly and we can provide a link or add it to your order.

Will this work with at&t sb67138 4-line corded-cordless phone system ?

Just for a ringing horn yes. If you're wanting to voice page and your system doesn't have a paging port then no

Please provide the links for whatever I need to make this work with my 8x8 voip phone system

This WOULD work with VoIP. You need a VoIP to analog convertor such as OBi300. You can see a list of adapters here: https://www.8x8.com/communications-solutions/equipment/adapters, however, there are more that work if you are willing to figure it out yourself.